Level 3: A first failed attempt of encoding-decoding -> SNR=0

source/core/aac_coder.py

@@ -9,8 +9,16 @@
 #   cchoutou@ece.auth.gr
 #
 # Description:
-#   - Level 1 AAC encoder orchestration.
+#   Level 1 AAC encoder orchestration.
-#   - Level 2 AAC encoder orchestration.
+#   Keeps the same functional behavior as the original level_1 implementation:
+#   - Reads WAV via soundfile
+#   - Validates stereo and 48 kHz
+#   - Frames into 2048 samples with hop=1024 and zero padding at both ends
+#   - SSC decision uses next-frame attack detection
+#   - Filterbank analysis (MDCT)
+#   - Stores per-channel spectra in AACSeq1 schema:
+#       * ESH: (128, 8)
+#       * else: (1024, 1)
 # ------------------------------------------------------------
 from __future__ import annotations
 
@@ -18,14 +26,106 @@ from pathlib import Path
 from typing import Union
 
 import soundfile as sf
+from scipy.io import savemat
 
 from core.aac_configuration import WIN_TYPE
 from core.aac_filterbank import aac_filter_bank
-from core.aac_ssc import aac_SSC
+from core.aac_ssc import aac_ssc
 from core.aac_tns import aac_tns
+from core.aac_psycho import aac_psycho
+from core.aac_quantizer import aac_quantizer  # assumes your quantizer file is core/aac_quantizer.py
+from core.aac_huffman import aac_encode_huff
+from core.aac_utils import get_table, band_limits
+from material.huff_utils import load_LUT
+
 from core.aac_types import *
 
 
+
+# -----------------------------------------------------------------------------
+# Helpers for thresholds (T(b))
+# -----------------------------------------------------------------------------
+
+def _band_slices_from_table(frame_type: FrameType) -> list[tuple[int, int]]:
+    """
+    Return inclusive (lo, hi) band slices derived from TableB219.
+    """
+    table, _ = get_table(frame_type)
+    wlow, whigh, _bval, _qthr_db = band_limits(table)
+    return [(int(lo), int(hi)) for lo, hi in zip(wlow, whigh)]
+
+
+def _thresholds_from_smr(
+    frame_F_ch: FrameChannelF,
+    frame_type: FrameType,
+    SMR: FloatArray,
+) -> FloatArray:
+    """
+    Compute thresholds T(b) = P(b) / SMR(b), where P(b) is band energy.
+
+    Shapes:
+    - Long: returns (NB, 1)
+    - ESH: returns (NB, 8)
+    """
+    bands = _band_slices_from_table(frame_type)
+    NB = len(bands)
+
+    X = np.asarray(frame_F_ch, dtype=np.float64)
+    SMR = np.asarray(SMR, dtype=np.float64)
+
+    if frame_type == "ESH":
+        if X.shape != (128, 8):
+            raise ValueError("For ESH, frame_F_ch must have shape (128, 8).")
+        if SMR.shape != (NB, 8):
+            raise ValueError(f"For ESH, SMR must have shape ({NB}, 8).")
+
+        T = np.zeros((NB, 8), dtype=np.float64)
+        for j in range(8):
+            Xj = X[:, j]
+            for b, (lo, hi) in enumerate(bands):
+                P = float(np.sum(Xj[lo : hi + 1] ** 2))
+                smr = float(SMR[b, j])
+                T[b, j] = 0.0 if smr <= 1e-12 else (P / smr)
+        return T
+
+    # Long
+    if X.shape == (1024,):
+        Xv = X
+    elif X.shape == (1024, 1):
+        Xv = X[:, 0]
+    else:
+        raise ValueError("For non-ESH, frame_F_ch must be shape (1024,) or (1024, 1).")
+
+    if SMR.shape == (NB,):
+        SMRv = SMR
+    elif SMR.shape == (NB, 1):
+        SMRv = SMR[:, 0]
+    else:
+        raise ValueError(f"For non-ESH, SMR must be shape ({NB},) or ({NB}, 1).")
+
+    T = np.zeros((NB, 1), dtype=np.float64)
+    for b, (lo, hi) in enumerate(bands):
+        P = float(np.sum(Xv[lo : hi + 1] ** 2))
+        smr = float(SMRv[b])
+        T[b, 0] = 0.0 if smr <= 1e-12 else (P / smr)
+
+    return T
+
+def _normalize_global_gain(G: GlobalGain) -> float | FloatArray:
+    """
+    Normalize GlobalGain to match AACChannelFrameF3["G"] type:
+    - long: return float
+    - ESH: return float64 ndarray of shape (1, 8)
+    """
+    if np.isscalar(G):
+        return float(G)
+
+    G_arr = np.asarray(G)
+    if G_arr.size == 1:
+        return float(G_arr.reshape(-1)[0])
+
+    return np.asarray(G_arr, dtype=np.float64)
+
 # -----------------------------------------------------------------------------
 # Public helpers (useful for level_x demo wrappers)
 # -----------------------------------------------------------------------------
@@ -174,7 +274,7 @@ def aac_coder_1(filename_in: Union[str, Path]) -> AACSeq1:
             tail = np.zeros((win - next_t.shape[0], 2), dtype=np.float64)
             next_t = np.vstack([next_t, tail])
 
-        frame_type = aac_SSC(frame_t, next_t, prev_frame_type)
+        frame_type = aac_ssc(frame_t, next_t, prev_frame_type)
         frame_f = aac_filter_bank(frame_t, frame_type, win_type)
 
         chl_f, chr_f = aac_pack_frame_f_to_seq_channels(frame_type, frame_f)
@@ -191,10 +291,6 @@ def aac_coder_1(filename_in: Union[str, Path]) -> AACSeq1:
     return aac_seq
 
 
-# -----------------------------------------------------------------------------
-# Level 2 encoder
-# -----------------------------------------------------------------------------
-
 def aac_coder_2(filename_in: Union[str, Path]) -> AACSeq2:
     """
     Level-2 AAC encoder (Level 1 + TNS).
@@ -246,7 +342,7 @@ def aac_coder_2(filename_in: Union[str, Path]) -> AACSeq2:
             tail = np.zeros((win - next_t.shape[0], 2), dtype=np.float64)
             next_t = np.vstack([next_t, tail])
 
-        frame_type = aac_SSC(frame_t, next_t, prev_frame_type)
+        frame_type = aac_ssc(frame_t, next_t, prev_frame_type)
 
         # Level 1 analysis (packed stereo container)
         frame_f_stereo = aac_filter_bank(frame_t, frame_type, WIN_TYPE)
@@ -278,3 +374,180 @@ def aac_coder_2(filename_in: Union[str, Path]) -> AACSeq2:
         prev_frame_type = frame_type
 
     return aac_seq
+
+
+def aac_coder_3(
+    filename_in: Union[str, Path],
+    filename_aac_coded: Union[str, Path] | None = None,
+) -> AACSeq3:
+    """
+    Level-3 AAC encoder (Level 2 + Psycho + Quantizer + Huffman).
+
+    Parameters
+    ----------
+    filename_in : Union[str, Path]
+        Input WAV filename (stereo, 48 kHz).
+    filename_aac_coded : Union[str, Path] | None
+        Optional .mat filename to store aac_seq_3 (assignment convenience).
+
+    Returns
+    -------
+    AACSeq3
+        Encoded AAC sequence (Level 3 payload schema).
+    """
+    filename_in = Path(filename_in)
+
+    x, _ = aac_read_wav_stereo_48k(filename_in)
+
+    hop = 1024
+    win = 2048
+
+    pad_pre = np.zeros((hop, 2), dtype=np.float64)
+    pad_post = np.zeros((hop, 2), dtype=np.float64)
+    x_pad = np.vstack([pad_pre, x, pad_post])
+
+    K = int((x_pad.shape[0] - win) // hop + 1)
+    if K <= 0:
+        raise ValueError("Input too short for framing.")
+
+    # Load Huffman LUTs once.
+    huff_LUT_list = load_LUT()
+
+    aac_seq: AACSeq3 = []
+    prev_frame_type: FrameType = "OLS"
+
+    # Pin win_type to the WinType literal for type checkers.
+    win_type: WinType = WIN_TYPE
+
+    # Psycho model needs per-channel history (prev1, prev2) of 2048-sample frames.
+    prev1_L = np.zeros((2048,), dtype=np.float64)
+    prev2_L = np.zeros((2048,), dtype=np.float64)
+    prev1_R = np.zeros((2048,), dtype=np.float64)
+    prev2_R = np.zeros((2048,), dtype=np.float64)
+
+    for i in range(K):
+        start = i * hop
+
+        frame_t: FrameT = x_pad[start : start + win, :]
+        if frame_t.shape != (win, 2):
+            raise ValueError("Internal framing error: frame_t has wrong shape.")
+
+        next_t = x_pad[start + hop : start + hop + win, :]
+        if next_t.shape[0] < win:
+            tail = np.zeros((win - next_t.shape[0], 2), dtype=np.float64)
+            next_t = np.vstack([next_t, tail])
+
+        frame_type = aac_ssc(frame_t, next_t, prev_frame_type)
+
+        # Analysis filterbank (stereo packed)
+        frame_f_stereo = aac_filter_bank(frame_t, frame_type, win_type)
+        chl_f, chr_f = aac_pack_frame_f_to_seq_channels(frame_type, frame_f_stereo)
+
+        # TNS per channel
+        chl_f_tns, chl_tns_coeffs = aac_tns(chl_f, frame_type)
+        chr_f_tns, chr_tns_coeffs = aac_tns(chr_f, frame_type)
+
+        # Psychoacoustic model per channel (time-domain)
+        frame_L = np.asarray(frame_t[:, 0], dtype=np.float64)
+        frame_R = np.asarray(frame_t[:, 1], dtype=np.float64)
+
+        SMR_L = aac_psycho(frame_L, frame_type, prev1_L, prev2_L)
+        SMR_R = aac_psycho(frame_R, frame_type, prev1_R, prev2_R)
+
+        # Thresholds T(b) (stored, not entropy-coded)
+        T_L = _thresholds_from_smr(chl_f_tns, frame_type, SMR_L)
+        T_R = _thresholds_from_smr(chr_f_tns, frame_type, SMR_R)
+
+        # Quantizer per channel
+        S_L, sfc_L, G_L = aac_quantizer(chl_f_tns, frame_type, SMR_L)
+        S_R, sfc_R, G_R = aac_quantizer(chr_f_tns, frame_type, SMR_R)
+
+        # Normalize G types for AACSeq3 schema (float | float64 ndarray).
+        G_Ln = _normalize_global_gain(G_L)
+        G_Rn = _normalize_global_gain(G_R)
+
+        # Huffman-code ONLY the DPCM differences for b>0.
+        # sfc[0] corresponds to alpha(0)=G and is stored separately in the frame.
+        sfc_L_dpcm = np.asarray(sfc_L, dtype=np.int64)[1:, ...]
+        sfc_R_dpcm = np.asarray(sfc_R, dtype=np.int64)[1:, ...]
+
+        # Codebook 11:
+        # maxAbsCodeVal = 16 is RESERVED for ESCAPE.
+        # We must stay strictly within [-15, +15] to avoid escape decoding.
+        sf_cb = 11
+        sf_max_abs = int(huff_LUT_list[sf_cb]["maxAbsCodeVal"]) - 1  # -> 15
+
+        sfc_L_dpcm = np.clip(
+            sfc_L_dpcm,
+            -sf_max_abs,
+            sf_max_abs,
+        ).astype(np.int64, copy=False)
+
+        sfc_R_dpcm = np.clip(
+            sfc_R_dpcm,
+            -sf_max_abs,
+            sf_max_abs,
+        ).astype(np.int64, copy=False)
+
+        sfc_L_stream, _ = aac_encode_huff(
+            sfc_L_dpcm.reshape(-1, order="F"),
+            huff_LUT_list,
+            force_codebook=sf_cb,
+        )
+        sfc_R_stream, _ = aac_encode_huff(
+            sfc_R_dpcm.reshape(-1, order="F"),
+            huff_LUT_list,
+            force_codebook=sf_cb,
+        )
+
+        mdct_L_stream, cb_L = aac_encode_huff(
+            np.asarray(S_L, dtype=np.int64).reshape(-1),
+            huff_LUT_list,
+        )
+        mdct_R_stream, cb_R = aac_encode_huff(
+            np.asarray(S_R, dtype=np.int64).reshape(-1),
+            huff_LUT_list,
+        )
+
+        # Typed dict construction helps static analyzers validate the schema.
+        frame_out: AACSeq3Frame = {
+            "frame_type": frame_type,
+            "win_type": win_type,
+            "chl": {
+                "tns_coeffs": np.asarray(chl_tns_coeffs, dtype=np.float64),
+                "T": np.asarray(T_L, dtype=np.float64),
+                "G": G_Ln,
+                "sfc": sfc_L_stream,
+                "stream": mdct_L_stream,
+                "codebook": int(cb_L),
+            },
+            "chr": {
+                "tns_coeffs": np.asarray(chr_tns_coeffs, dtype=np.float64),
+                "T": np.asarray(T_R, dtype=np.float64),
+                "G": G_Rn,
+                "sfc": sfc_R_stream,
+                "stream": mdct_R_stream,
+                "codebook": int(cb_R),
+            },
+        }
+        aac_seq.append(frame_out)
+
+        # Update psycho history (shift register)
+        prev2_L = prev1_L
+        prev1_L = frame_L
+        prev2_R = prev1_R
+        prev1_R = frame_R
+
+        prev_frame_type = frame_type
+
+    # Optional: store to .mat for the assignment wrapper
+    if filename_aac_coded is not None:
+        filename_aac_coded = Path(filename_aac_coded)
+        savemat(
+            str(filename_aac_coded),
+            {"aac_seq_3": np.array(aac_seq, dtype=object)},
+            do_compression=True,
+        )
+
+    return aac_seq
+

source/core/aac_decoder.py

@@ -22,9 +22,22 @@ import soundfile as sf
 
 from core.aac_filterbank import aac_i_filter_bank
 from core.aac_tns import aac_i_tns
+from core.aac_quantizer import aac_i_quantizer
+from core.aac_huffman import aac_decode_huff
+from core.aac_utils import get_table, band_limits
+from material.huff_utils import load_LUT
 from core.aac_types import *
 
 
+# -----------------------------------------------------------------------------
+# Helper for NB
+# -----------------------------------------------------------------------------
+def _nbands(frame_type: FrameType) -> int:
+    table, _ = get_table(frame_type)
+    wlow, _whigh, _bval, _qthr_db = band_limits(table)
+    return int(len(wlow))
+
+
 # -----------------------------------------------------------------------------
 # Public helpers
 # -----------------------------------------------------------------------------
@@ -252,3 +265,144 @@ def aac_decoder_2(aac_seq_2: AACSeq2, filename_out: Union[str, Path]) -> StereoS
 
     sf.write(str(filename_out), y, 48000)
     return y
+
+
+
+def aac_decoder_3(aac_seq_3: AACSeq3, filename_out: Union[str, Path]) -> StereoSignal:
+    """
+    Level-3 AAC decoder (inverse of aac_coder_3).
+
+    Steps per frame:
+    - Huffman decode scalefactors (sfc) using codebook 11
+    - Huffman decode MDCT symbols (stream) using stored codebook
+    - iQuantizer -> MDCT coefficients after TNS
+    - iTNS using stored predictor coefficients
+    - IMDCT filterbank -> time domain
+    - Overlap-add, remove padding, write WAV
+
+    Parameters
+    ----------
+    aac_seq_3 : AACSeq3
+        Encoded sequence as produced by aac_coder_3.
+    filename_out : Union[str, Path]
+        Output WAV filename.
+
+    Returns
+    -------
+    StereoSignal
+        Decoded audio samples (time-domain), stereo, shape (N, 2), dtype float64.
+    """
+    filename_out = Path(filename_out)
+
+    hop = 1024
+    win = 2048
+    K = len(aac_seq_3)
+
+    if K <= 0:
+        raise ValueError("aac_seq_3 must contain at least one frame.")
+
+    # Load Huffman LUTs once.
+    huff_LUT_list = load_LUT()
+
+    n_pad = (K - 1) * hop + win
+    y_pad = np.zeros((n_pad, 2), dtype=np.float64)
+
+    for i, fr in enumerate(aac_seq_3):
+        frame_type: FrameType = fr["frame_type"]
+        win_type: WinType = fr["win_type"]
+
+        NB = _nbands(frame_type)
+        # We store G separately, so Huffman stream contains only (NB-1) DPCM differences.
+        sfc_len = (NB - 1) * (8 if frame_type == "ESH" else 1)
+
+        # -------------------------
+        # Left channel
+        # -------------------------
+        tns_L = np.asarray(fr["chl"]["tns_coeffs"], dtype=np.float64)
+        G_L = fr["chl"]["G"]
+        sfc_bits_L = fr["chl"]["sfc"]
+        mdct_bits_L = fr["chl"]["stream"]
+        cb_L = int(fr["chl"]["codebook"])
+
+        sfc_dec_L = aac_decode_huff(sfc_bits_L, 11, huff_LUT_list)[:sfc_len].astype(np.int64, copy=False)
+        if frame_type == "ESH":
+            sfc_dpcm_L = sfc_dec_L.reshape(NB - 1, 8, order="F")
+            sfc_L = np.zeros((NB, 8), dtype=np.int64)
+            Gv = np.asarray(G_L, dtype=np.float64).reshape(1, 8)
+            sfc_L[0, :] = Gv[0, :].astype(np.int64)
+            sfc_L[1:, :] = sfc_dpcm_L
+        else:
+            sfc_dpcm_L = sfc_dec_L.reshape(NB - 1, 1, order="F")
+            sfc_L = np.zeros((NB, 1), dtype=np.int64)
+            sfc_L[0, 0] = int(float(G_L))
+            sfc_L[1:, :] = sfc_dpcm_L
+
+        # MDCT symbols: codebook 0 means "all-zero section"
+        if cb_L == 0:
+            S_dec_L = np.zeros((1024,), dtype=np.int64)
+        else:
+            S_tmp_L = aac_decode_huff(mdct_bits_L, cb_L, huff_LUT_list).astype(np.int64, copy=False)
+
+            # Tuple coding may produce extra trailing symbols; caller knows the true length (1024).
+            # Also guard against short outputs by zero-padding.
+            if S_tmp_L.size < 1024:
+                S_dec_L = np.zeros((1024,), dtype=np.int64)
+                S_dec_L[: S_tmp_L.size] = S_tmp_L
+            else:
+                S_dec_L = S_tmp_L[:1024]
+
+        S_L = S_dec_L.reshape(1024, 1)
+
+        Xq_L = aac_i_quantizer(S_L, sfc_L, G_L, frame_type)
+        X_L = aac_i_tns(Xq_L, frame_type, tns_L)
+
+        # -------------------------
+        # Right channel
+        # -------------------------
+        tns_R = np.asarray(fr["chr"]["tns_coeffs"], dtype=np.float64)
+        G_R = fr["chr"]["G"]
+        sfc_bits_R = fr["chr"]["sfc"]
+        mdct_bits_R = fr["chr"]["stream"]
+        cb_R = int(fr["chr"]["codebook"])
+
+        sfc_dec_R = aac_decode_huff(sfc_bits_R, 11, huff_LUT_list)[:sfc_len].astype(np.int64, copy=False)
+        if frame_type == "ESH":
+            sfc_dpcm_R = sfc_dec_R.reshape(NB - 1, 8, order="F")
+            sfc_R = np.zeros((NB, 8), dtype=np.int64)
+            Gv = np.asarray(G_R, dtype=np.float64).reshape(1, 8)
+            sfc_R[0, :] = Gv[0, :].astype(np.int64)
+            sfc_R[1:, :] = sfc_dpcm_R
+        else:
+            sfc_dpcm_R = sfc_dec_R.reshape(NB - 1, 1, order="F")
+            sfc_R = np.zeros((NB, 1), dtype=np.int64)
+            sfc_R[0, 0] = int(float(G_R))
+            sfc_R[1:, :] = sfc_dpcm_R
+
+        if cb_R == 0:
+            S_dec_R = np.zeros((1024,), dtype=np.int64)
+        else:
+            S_tmp_R = aac_decode_huff(mdct_bits_R, cb_R, huff_LUT_list).astype(np.int64, copy=False)
+
+            if S_tmp_R.size < 1024:
+                S_dec_R = np.zeros((1024,), dtype=np.int64)
+                S_dec_R[: S_tmp_R.size] = S_tmp_R
+            else:
+                S_dec_R = S_tmp_R[:1024]
+
+        S_R = S_dec_R.reshape(1024, 1)
+
+        Xq_R = aac_i_quantizer(S_R, sfc_R, G_R, frame_type)
+        X_R = aac_i_tns(Xq_R, frame_type, tns_R)
+
+        # Re-pack to stereo container and inverse filterbank
+        frame_f = aac_unpack_seq_channels_to_frame_f(frame_type, np.asarray(X_L), np.asarray(X_R))
+        frame_t_hat: FrameT = aac_i_filter_bank(frame_f, frame_type, win_type)
+
+        start = i * hop
+        y_pad[start : start + win, :] += frame_t_hat
+
+    y = aac_remove_padding(y_pad, hop=hop)
+
+    sf.write(str(filename_out), y, 48000)
+    return y
+

source/core/aac_huffman.py

@@ -0,0 +1,112 @@
+# ------------------------------------------------------------
+# AAC Coder/Decoder - Huffman wrappers (Level 3)
+#
+# Multimedia course at Aristotle University of
+# Thessaloniki (AUTh)
+#
+# Author:
+#   Christos Choutouridis (ΑΕΜ 8997)
+#   cchoutou@ece.auth.gr
+#
+# Description:
+#   Thin wrappers around the provided Huffman utilities (material/huff_utils.py)
+#   so that the API matches the assignment text.
+#
+# Exposed API (assignment):
+#   huff_sec, huff_codebook = aac_encode_huff(coeff_sec, huff_LUT_list, force_codebook)
+#   dec_coeffs = aac_decode_huff(huff_sec, huff_codebook, huff_LUT_list)
+#
+# Notes:
+#   - Huffman coding operates on tuples. Therefore, decode(encode(x)) may return
+#     extra trailing symbols due to tuple padding. The AAC decoder knows the
+#     true section length from side information (band limits) and truncates.
+# ------------------------------------------------------------
+from __future__ import annotations
+
+from typing import Any
+import numpy as np
+
+from material.huff_utils import encode_huff, decode_huff
+
+
+def aac_encode_huff(
+    coeff_sec: np.ndarray,
+    huff_LUT_list: list[dict[str, Any]],
+    force_codebook: int | None = None,
+) -> tuple[str, int]:
+    """
+    Huffman-encode a section of coefficients (MDCT symbols or scalefactors).
+
+    Parameters
+    ----------
+    coeff_sec : np.ndarray
+        Coefficient section to be encoded. Any shape is accepted; the input
+        is flattened and treated as a 1-D sequence of int64 symbols.
+    huff_LUT_list : list[dict[str, Any]]
+        List of Huffman Look-Up Tables (LUTs) as returned by material.load_LUT().
+        Index corresponds to codebook id (typically 1..11, with 0 reserved).
+    force_codebook : int | None
+        If provided, forces the use of this Huffman codebook. In the assignment,
+        scalefactors are encoded with codebook 11. For MDCT coefficients, this
+        argument is usually omitted (auto-selection).
+
+    Returns
+    -------
+    tuple[str, int]
+        (huff_sec, huff_codebook)
+        - huff_sec: bitstream as a string of '0'/'1'
+        - huff_codebook: codebook id used by the encoder
+    """
+    coeff_sec_arr = np.asarray(coeff_sec, dtype=np.int64).reshape(-1)
+
+    if force_codebook is None:
+        # Provided utility returns (bitstream, codebook) in the auto-selection case.
+        huff_sec, huff_codebook = encode_huff(coeff_sec_arr, huff_LUT_list)
+        return str(huff_sec), int(huff_codebook)
+
+    # Provided utility returns ONLY the bitstream when force_codebook is set.
+    cb = int(force_codebook)
+    huff_sec = encode_huff(coeff_sec_arr, huff_LUT_list, force_codebook=cb)
+    return str(huff_sec), cb
+
+
+def aac_decode_huff(
+    huff_sec: str | np.ndarray,
+    huff_codebook: int,
+    huff_LUT: list[dict[str, Any]],
+) -> np.ndarray:
+    """
+    Huffman-decode a bitstream using the specified codebook.
+
+    Parameters
+    ----------
+    huff_sec : str | np.ndarray
+        Huffman bitstream. Typically a string of '0'/'1'. If an array is provided,
+        it is passed through to the provided decoder.
+    huff_codebook : int
+        Codebook id that was returned by aac_encode_huff.
+        Codebook 0 represents an all-zero section.
+    huff_LUT : list[dict[str, Any]]
+        Huffman LUT list as returned by material.load_LUT().
+
+    Returns
+    -------
+    np.ndarray
+        Decoded coefficients as a 1-D np.int64 array.
+
+        Note: Due to tuple coding, the decoded array may contain extra trailing
+        padding symbols. The caller must truncate to the known section length.
+    """
+    cb = int(huff_codebook)
+
+    if cb == 0:
+        # Codebook 0 represents an all-zero section. The decoded length is not
+        # recoverable from the bitstream alone; the caller must expand/truncate.
+        return np.zeros((0,), dtype=np.int64)
+
+    if cb < 0 or cb >= len(huff_LUT):
+        raise ValueError(f"Invalid Huffman codebook index: {cb}")
+
+    lut = huff_LUT[cb]
+    dec = decode_huff(huff_sec, lut)
+    return np.asarray(dec, dtype=np.int64).reshape(-1)

source/core/aac_quantizer.py

@@ -0,0 +1,604 @@
+# ------------------------------------------------------------
+# AAC Coder/Decoder - Quantizer / iQuantizer (Level 3)
+#
+# Multimedia course at Aristotle University of
+# Thessaloniki (AUTh)
+#
+# Author:
+#   Christos Choutouridis (ΑΕΜ 8997)
+#   cchoutou@ece.auth.gr
+#
+# Description:
+#   Implements AAC quantizer and inverse quantizer for one channel.
+#   Based on assignment section 2.6 (Eq. 12-15).
+#
+# Notes:
+#   - Bit reservoir is not implemented (assignment simplification).
+#   - Scalefactor bands are assumed equal to psychoacoustic bands
+#     (Table B.2.1.9a / B.2.1.9b from TableB219.mat).
+# ------------------------------------------------------------
+from __future__ import annotations
+
+import numpy as np
+
+from core.aac_utils import get_table, band_limits
+from core.aac_types import *
+
+# -----------------------------------------------------------------------------
+# Constants (assignment)
+# -----------------------------------------------------------------------------
+MAGIC_NUMBER: float = 0.4054
+MQ: int = 8191
+
+EPS: float = 1e-12
+MAX_SFC_DIFF: int = 60
+
+# Safeguard: prevents infinite loops in pathological cases
+MAX_ALPHA_ITERS: int = 2000
+
+
+# -----------------------------------------------------------------------------
+# Helpers: ESH packing/unpacking (128x8 <-> 1024x1)
+# -----------------------------------------------------------------------------
+def _esh_pack_to_1024(x_128x8: FloatArray) -> FloatArray:
+    """
+    Pack ESH coefficients (128 x 8) into a single long vector (1024 x 1).
+
+    Packing order:
+        Columns are concatenated in subframe order (0..7), column-major.
+
+    Parameters
+    ----------
+    x_128x8 : FloatArray
+        ESH coefficients, shape (128, 8).
+
+    Returns
+    -------
+    FloatArray
+        Packed coefficients, shape (1024, 1).
+    """
+    x_128x8 = np.asarray(x_128x8, dtype=np.float64)
+    if x_128x8.shape != (128, 8):
+        raise ValueError("ESH pack expects shape (128, 8).")
+    return x_128x8.reshape(1024, 1, order="F")
+
+
+def _esh_unpack_from_1024(x_1024x1: FloatArray) -> FloatArray:
+    """
+    Unpack a packed ESH vector (1024 elements) back to shape (128, 8).
+
+    Parameters
+    ----------
+    x_1024x1 : FloatArray
+        Packed ESH vector, shape (1024,) or (1024, 1) after flattening.
+
+    Returns
+    -------
+    FloatArray
+        Unpacked ESH coefficients, shape (128, 8).
+    """
+    x_1024x1 = np.asarray(x_1024x1, dtype=np.float64).reshape(-1)
+    if x_1024x1.shape[0] != 1024:
+        raise ValueError("ESH unpack expects 1024 elements.")
+    return x_1024x1.reshape(128, 8, order="F")
+
+
+# -----------------------------------------------------------------------------
+# Core quantizer formulas (Eq. 12, Eq. 13)
+# -----------------------------------------------------------------------------
+def _quantize_symbol(x: FloatArray, alpha: float) -> QuantizedSymbols:
+    """
+    Quantize MDCT coefficients to integer symbols S(k).
+
+    Implements Eq. (12):
+        S(k) = sgn(X(k)) * int( (|X(k)| * 2^(-alpha/4))^(3/4) + MAGIC_NUMBER )
+
+    Parameters
+    ----------
+    x : FloatArray
+        MDCT coefficients for a contiguous set of spectral lines.
+        Shape: (N,)
+    alpha : float
+        Scalefactor gain for the corresponding scalefactor band.
+
+    Returns
+    -------
+    QuantizedSymbols
+        Quantized symbols S(k) as int64, shape (N,).
+    """
+    x = np.asarray(x, dtype=np.float64)
+
+    scale = 2.0 ** (-0.25 * float(alpha))
+    ax = np.abs(x) * scale
+
+    y = np.power(ax, 0.75, dtype=np.float64)
+
+    # "int" in the assignment corresponds to truncation.
+    q = np.floor(y + MAGIC_NUMBER).astype(np.int64)
+    return (np.sign(x).astype(np.int64) * q).astype(np.int64)
+
+
+def _dequantize_symbol(S: QuantizedSymbols, alpha: float) -> FloatArray:
+    """
+    Inverse quantizer (dequantization of symbols).
+
+    Implements Eq. (13):
+        Xhat(k) = sgn(S(k)) * |S(k)|^(4/3) * 2^(alpha/4)
+
+    Parameters
+    ----------
+    S : QuantizedSymbols
+        Quantized symbols S(k), int64, shape (N,).
+    alpha : float
+        Scalefactor gain for the corresponding scalefactor band.
+
+    Returns
+    -------
+    FloatArray
+        Reconstructed MDCT coefficients Xhat(k), float64, shape (N,).
+    """
+    S = np.asarray(S, dtype=np.int64)
+
+    scale = 2.0 ** (0.25 * float(alpha))
+    aS = np.abs(S).astype(np.float64)
+    y = np.power(aS, 4.0 / 3.0, dtype=np.float64)
+
+    return (np.sign(S).astype(np.float64) * y * scale).astype(np.float64)
+
+
+# -----------------------------------------------------------------------------
+# Alpha initialization (Eq. 14)
+# -----------------------------------------------------------------------------
+def _alpha_initial_from_frame_max(x_all: FloatArray) -> int:
+    """
+    Compute the initial scalefactor gain alpha_hat for a frame.
+
+    Implements Eq. (14):
+        alpha_hat = (16/3) * log2( max_k(|X(k)|^(3/4)) / MQ )
+
+    The same initial value is used for all bands before the per-band refinement.
+
+    Parameters
+    ----------
+    x_all : FloatArray
+        All MDCT coefficients of a frame (one channel), flattened.
+
+    Returns
+    -------
+    int
+        Initial alpha value (integer).
+    """
+    x_all = np.asarray(x_all, dtype=np.float64).reshape(-1)
+    if x_all.size == 0:
+        return 0
+
+    max_abs = float(np.max(np.abs(x_all)))
+    if max_abs <= 0.0:
+        return 0
+
+    val = (max_abs ** 0.75) / float(MQ)
+    if val <= 0.0:
+        return 0
+
+    alpha_hat = (16.0 / 3.0) * np.log2(val)
+    return int(np.floor(alpha_hat))
+
+
+# -----------------------------------------------------------------------------
+# Band utilities
+# -----------------------------------------------------------------------------
+def _band_slices(frame_type: FrameType) -> list[tuple[int, int]]:
+    """
+    Return scalefactor band ranges [wlow, whigh] (inclusive) for the given frame type.
+
+    These are derived from the psychoacoustic tables (TableB219),
+    and map directly to MDCT indices:
+      - long: 0..1023
+      - short (ESH subframe): 0..127
+
+    Parameters
+    ----------
+    frame_type : FrameType
+        Frame type ("OLS", "LSS", "ESH", "LPS").
+
+    Returns
+    -------
+    list[tuple[int, int]]
+        List of (lo, hi) inclusive index pairs for each band.
+    """
+    table, _Nfft = get_table(frame_type)
+    wlow, whigh, _bval, _qthr_db = band_limits(table)
+
+    bands: list[tuple[int, int]] = []
+    for lo, hi in zip(wlow, whigh):
+        bands.append((int(lo), int(hi)))
+    return bands
+
+
+def _band_energy(x: FloatArray, lo: int, hi: int) -> float:
+    """
+    Compute energy of a spectral segment x[lo:hi+1].
+
+    Parameters
+    ----------
+    x : FloatArray
+        MDCT coefficient vector.
+    lo, hi : int
+        Inclusive index range.
+
+    Returns
+    -------
+    float
+        Sum of squares (energy) within the band.
+    """
+    sec = x[lo : hi + 1]
+    return float(np.sum(sec * sec))
+
+
+def _threshold_T_from_SMR(
+    X: FloatArray,
+    SMR_col: FloatArray,
+    bands: list[tuple[int, int]],
+) -> FloatArray:
+    """
+    Compute psychoacoustic thresholds T(b) per band.
+
+    Uses:
+        P(b) = sum_{k in band} X(k)^2
+        T(b) = P(b) / SMR(b)
+
+    Parameters
+    ----------
+    X : FloatArray
+        MDCT coefficients for a frame (long) or one ESH subframe (short).
+    SMR_col : FloatArray
+        SMR values for this frame/subframe, shape (NB,).
+    bands : list[tuple[int, int]]
+        Band index ranges.
+
+    Returns
+    -------
+    FloatArray
+        Threshold vector T(b), shape (NB,).
+    """
+    nb = len(bands)
+    T = np.zeros((nb,), dtype=np.float64)
+
+    for b, (lo, hi) in enumerate(bands):
+        P = _band_energy(X, lo, hi)
+        smr = float(SMR_col[b])
+        if smr <= EPS:
+            T[b] = 0.0
+        else:
+            T[b] = P / smr
+
+    return T
+
+
+# -----------------------------------------------------------------------------
+# Alpha selection per band + neighbor-difference constraint
+# -----------------------------------------------------------------------------
+def _best_alpha_for_band(
+    X: FloatArray,
+    lo: int,
+    hi: int,
+    T_b: float,
+    alpha0: int,
+    alpha_min: int,
+    alpha_max: int,
+) -> int:
+    """
+    Determine the band-wise scalefactor alpha(b) by iteratively increasing alpha.
+
+    The algorithm increases alpha until the quantization error power exceeds
+    the band threshold:
+
+        P_e(b) = sum_{k in band} (X(k) - Xhat(k))^2
+        select the largest alpha such that P_e(b) <= T(b)
+
+    Parameters
+    ----------
+    X : FloatArray
+        Full MDCT vector (one frame or one subframe), shape (N,).
+    lo, hi : int
+        Inclusive MDCT index range defining the band.
+    T_b : float
+        Psychoacoustic threshold for this band.
+    alpha0 : int
+        Initial alpha value for the band.
+    alpha_min, alpha_max : int
+        Bounds for alpha, used as a safeguard.
+
+    Returns
+    -------
+    int
+        Selected integer alpha(b).
+    """
+    if T_b <= 0.0:
+        return int(alpha0)
+
+    Xsec = X[lo : hi + 1]
+
+    alpha = int(alpha0)
+    alpha = max(alpha_min, min(alpha, alpha_max))
+
+    # Evaluate at current alpha
+    Ssec = _quantize_symbol(Xsec, alpha)
+    Xhat = _dequantize_symbol(Ssec, alpha)
+    Pe = float(np.sum((Xsec - Xhat) ** 2))
+
+    if Pe > T_b:
+        return alpha
+
+    iters = 0
+    while iters < MAX_ALPHA_ITERS:
+        iters += 1
+        alpha_next = alpha + 1
+        if alpha_next > alpha_max:
+            break
+
+        Ssec = _quantize_symbol(Xsec, alpha_next)
+        Xhat = _dequantize_symbol(Ssec, alpha_next)
+        Pe_next = float(np.sum((Xsec - Xhat) ** 2))
+
+        if Pe_next > T_b:
+            break
+
+        alpha = alpha_next
+        Pe = Pe_next
+
+    return alpha
+
+
+def _enforce_max_diff(alpha: np.ndarray, max_diff: int = MAX_SFC_DIFF) -> np.ndarray:
+    """
+    Enforce neighbor constraint |alpha[b] - alpha[b-1]| <= max_diff by clamping.
+
+    Uses a forward pass and a backward pass to reduce drift.
+
+    Parameters
+    ----------
+    alpha : np.ndarray
+        Alpha vector, shape (NB,).
+    max_diff : int
+        Maximum allowed absolute difference between adjacent bands.
+
+    Returns
+    -------
+    np.ndarray
+        Clamped alpha vector, int64, shape (NB,).
+    """
+    a = np.asarray(alpha, dtype=np.int64).copy()
+    nb = a.shape[0]
+
+    for b in range(1, nb):
+        lo = int(a[b - 1] - max_diff)
+        hi = int(a[b - 1] + max_diff)
+        if a[b] < lo:
+            a[b] = lo
+        elif a[b] > hi:
+            a[b] = hi
+
+    for b in range(nb - 2, -1, -1):
+        lo = int(a[b + 1] - max_diff)
+        hi = int(a[b + 1] + max_diff)
+        if a[b] < lo:
+            a[b] = lo
+        elif a[b] > hi:
+            a[b] = hi
+
+    return a
+
+
+# -----------------------------------------------------------------------------
+# Public API
+# -----------------------------------------------------------------------------
+def aac_quantizer(
+    frame_F: FrameChannelF,
+    frame_type: FrameType,
+    SMR: FloatArray,
+) -> tuple[QuantizedSymbols, ScaleFactors, GlobalGain]:
+    """
+    AAC quantizer for one channel (Level 3).
+
+    Quantizes MDCT coefficients using band-wise scalefactors derived from SMR.
+
+    Parameters
+    ----------
+    frame_F : FrameChannelF
+        MDCT coefficients after TNS, one channel.
+        Shapes:
+        - Long frames: (1024,) or (1024, 1)
+        - ESH: (128, 8)
+    frame_type : FrameType
+        AAC frame type ("OLS", "LSS", "ESH", "LPS").
+    SMR : FloatArray
+        Signal-to-Mask Ratio per band.
+        Shapes:
+        - Long: (NB,) or (NB, 1)
+        - ESH: (NB, 8)
+
+    Returns
+    -------
+    S : QuantizedSymbols
+        Quantized symbols S(k), shape (1024, 1) for all frame types.
+    sfc : ScaleFactors
+        DPCM-coded scalefactor differences sfc(b) = alpha(b) - alpha(b-1).
+        Shapes:
+        - Long: (NB, 1)
+        - ESH: (NB, 8)
+    G : GlobalGain
+        Global gain G = alpha(0).
+        - Long: scalar float
+        - ESH: array shape (1, 8)
+    """
+    bands = _band_slices(frame_type)
+    NB = len(bands)
+
+    X = np.asarray(frame_F, dtype=np.float64)
+    SMR = np.asarray(SMR, dtype=np.float64)
+
+    if frame_type == "ESH":
+        if X.shape != (128, 8):
+            raise ValueError("For ESH, frame_F must have shape (128, 8).")
+        if SMR.shape != (NB, 8):
+            raise ValueError(f"For ESH, SMR must have shape ({NB}, 8).")
+
+        S_out: QuantizedSymbols = np.zeros((1024, 1), dtype=np.int64)
+        sfc: ScaleFactors = np.zeros((NB, 8), dtype=np.int64)
+        G_arr = np.zeros((1, 8), dtype=np.int64)
+
+        for j in range(8):
+            Xj = X[:, j].reshape(128)
+            SMRj = SMR[:, j].reshape(NB)
+
+            T = _threshold_T_from_SMR(Xj, SMRj, bands)
+
+            alpha0 = _alpha_initial_from_frame_max(Xj)
+            alpha = np.full((NB,), alpha0, dtype=np.int64)
+
+            for b, (lo, hi) in enumerate(bands):
+                alpha[b] = _best_alpha_for_band(
+                    X=Xj, lo=lo, hi=hi, T_b=float(T[b]),
+                    alpha0=int(alpha[b]),
+                    alpha_min=-4096,
+                    alpha_max=4096,
+                )
+
+            alpha = _enforce_max_diff(alpha, MAX_SFC_DIFF)
+
+            G_arr[0, j] = int(alpha[0])
+            sfc[0, j] = int(alpha[0])
+            for b in range(1, NB):
+                sfc[b, j] = int(alpha[b] - alpha[b - 1])
+
+            Sj = np.zeros((128,), dtype=np.int64)
+            for b, (lo, hi) in enumerate(bands):
+                Sj[lo : hi + 1] = _quantize_symbol(Xj[lo : hi + 1], float(alpha[b]))
+
+            # Place this subframe in the packed output (column-major subframe layout)
+            S_out[:, 0].reshape(128, 8, order="F")[:, j] = Sj
+
+        return S_out, sfc, G_arr.astype(np.float64)
+
+    # Long frames
+    if X.shape == (1024,):
+        Xv = X
+    elif X.shape == (1024, 1):
+        Xv = X[:, 0]
+    else:
+        raise ValueError("For non-ESH, frame_F must have shape (1024,) or (1024, 1).")
+
+    if SMR.shape == (NB,):
+        SMRv = SMR
+    elif SMR.shape == (NB, 1):
+        SMRv = SMR[:, 0]
+    else:
+        raise ValueError(f"For non-ESH, SMR must have shape ({NB},) or ({NB}, 1).")
+
+    T = _threshold_T_from_SMR(Xv, SMRv, bands)
+
+    alpha0 = _alpha_initial_from_frame_max(Xv)
+    alpha = np.full((NB,), alpha0, dtype=np.int64)
+
+    for b, (lo, hi) in enumerate(bands):
+        alpha[b] = _best_alpha_for_band(
+            X=Xv, lo=lo, hi=hi, T_b=float(T[b]),
+            alpha0=int(alpha[b]),
+            alpha_min=-4096,
+            alpha_max=4096,
+        )
+
+    alpha = _enforce_max_diff(alpha, MAX_SFC_DIFF)
+
+    sfc: ScaleFactors = np.zeros((NB, 1), dtype=np.int64)
+    sfc[0, 0] = int(alpha[0])
+    for b in range(1, NB):
+        sfc[b, 0] = int(alpha[b] - alpha[b - 1])
+
+    G: float = float(alpha[0])
+
+    S_vec = np.zeros((1024,), dtype=np.int64)
+    for b, (lo, hi) in enumerate(bands):
+        S_vec[lo : hi + 1] = _quantize_symbol(Xv[lo : hi + 1], float(alpha[b]))
+
+    return S_vec.reshape(1024, 1), sfc, G
+
+
+def aac_i_quantizer(
+    S: QuantizedSymbols,
+    sfc: ScaleFactors,
+    G: GlobalGain,
+    frame_type: FrameType,
+) -> FrameChannelF:
+    """
+    Inverse quantizer (iQuantizer) for one channel.
+
+    Reconstructs MDCT coefficients from quantized symbols and DPCM scalefactors.
+
+    Parameters
+    ----------
+    S : QuantizedSymbols
+        Quantized symbols, shape (1024, 1) (or any array with 1024 elements).
+    sfc : ScaleFactors
+        DPCM-coded scalefactors.
+        Shapes:
+        - Long: (NB, 1)
+        - ESH: (NB, 8)
+    G : GlobalGain
+        Global gain (not strictly required if sfc includes sfc(0)=alpha(0)).
+        Present for API compatibility with the assignment.
+    frame_type : FrameType
+        AAC frame type.
+
+    Returns
+    -------
+    FrameChannelF
+        Reconstructed MDCT coefficients:
+        - ESH: (128, 8)
+        - Long: (1024, 1)
+    """
+    bands = _band_slices(frame_type)
+    NB = len(bands)
+
+    S_flat = np.asarray(S, dtype=np.int64).reshape(-1)
+    if S_flat.shape[0] != 1024:
+        raise ValueError("S must contain 1024 symbols.")
+
+    if frame_type == "ESH":
+        sfc = np.asarray(sfc, dtype=np.int64)
+        if sfc.shape != (NB, 8):
+            raise ValueError(f"For ESH, sfc must have shape ({NB}, 8).")
+
+        S_128x8 = _esh_unpack_from_1024(S_flat)
+
+        Xrec = np.zeros((128, 8), dtype=np.float64)
+
+        for j in range(8):
+            alpha = np.zeros((NB,), dtype=np.int64)
+            alpha[0] = int(sfc[0, j])
+            for b in range(1, NB):
+                alpha[b] = int(alpha[b - 1] + sfc[b, j])
+
+            Xj = np.zeros((128,), dtype=np.float64)
+            for b, (lo, hi) in enumerate(bands):
+                Xj[lo : hi + 1] = _dequantize_symbol(S_128x8[lo : hi + 1, j].astype(np.int64), float(alpha[b]))
+
+            Xrec[:, j] = Xj
+
+        return Xrec
+
+    sfc = np.asarray(sfc, dtype=np.int64)
+    if sfc.shape != (NB, 1):
+        raise ValueError(f"For non-ESH, sfc must have shape ({NB}, 1).")
+
+    alpha = np.zeros((NB,), dtype=np.int64)
+    alpha[0] = int(sfc[0, 0])
+    for b in range(1, NB):
+        alpha[b] = int(alpha[b - 1] + sfc[b, 0])
+
+    Xrec = np.zeros((1024,), dtype=np.float64)
+    for b, (lo, hi) in enumerate(bands):
+        Xrec[lo : hi + 1] = _dequantize_symbol(S_flat[lo : hi + 1], float(alpha[b]))
+
+    return Xrec.reshape(1024, 1)

source/core/aac_ssc.py

@@ -176,7 +176,7 @@ def _stereo_merge(ft_l: FrameType, ft_r: FrameType) -> FrameType:
 # Public Function prototypes
 # -----------------------------------------------------------------------------
 
-def aac_SSC(frame_T: FrameT, next_frame_T: FrameT, prev_frame_type: FrameType) -> FrameType:
+def aac_ssc(frame_T: FrameT, next_frame_T: FrameT, prev_frame_type: FrameType) -> FrameType:
     """
     Sequence Segmentation Control (SSC).
 

source/core/aac_tns.py

@@ -30,9 +30,6 @@ from __future__ import annotations
 from pathlib import Path
 from typing import Tuple
 
-import numpy as np
-from scipy.io import loadmat
-
 from core.aac_utils import load_b219_tables
 from core.aac_configuration import PRED_ORDER, QUANT_STEP, QUANT_MAX
 from core.aac_types import *
@@ -377,7 +374,9 @@ def _tns_one_vector(x: MdctCoeffs) -> tuple[MdctCoeffs, MdctCoeffs]:
     sw = _compute_sw(x)
 
     eps = 1e-12
-    xw = np.where(sw > eps, x / sw, 0.0)
+    xw = np.zeros_like(x, dtype=np.float64)
+    mask = sw > eps
+    np.divide(x, sw, out=xw, where=mask)
 
     a = _lpc_coeffs(xw, PRED_ORDER)
     a_q = _quantize_coeffs(a)

source/core/aac_types.py

@@ -212,6 +212,42 @@ BandValueArray: TypeAlias = FloatArray
 Per-band psychoacoustic values (e.g. Bark position, thresholds).
 """
 
+
+# Quantizer-related semantic aliases
+
+QuantizedSymbols: TypeAlias = NDArray[np.generic]
+"""
+Quantized MDCT symbols S(k).
+
+Shapes:
+- Always (1024, 1) at the quantizer output (ESH packed to 1024 symbols).
+"""
+
+ScaleFactors: TypeAlias = NDArray[np.generic]
+"""
+DPCM-coded scalefactors sfc(b) = alpha(b) - alpha(b-1).
+
+Shapes:
+- Long frames: (NB, 1)
+- ESH frames: (NB, 8)
+"""
+
+GlobalGain: TypeAlias = float | NDArray[np.generic]
+"""
+Global gain G = alpha(0).
+
+- Long frames: scalar float
+- ESH frames: array shape (1, 8)
+"""
+
+# Huffman semantic aliases
+
+HuffmanBitstream: TypeAlias = str
+"""Huffman-coded bitstream stored as a string of '0'/'1'."""
+
+HuffmanCodebook: TypeAlias = int
+"""Huffman codebook id (e.g., 0..11)."""
+
 # -----------------------------------------------------------------------------
 # Level 1 AAC sequence payload types
 # -----------------------------------------------------------------------------
@@ -299,3 +335,77 @@ Level 2 adds:
 and stores:
 - per-channel "frame_F" after applying TNS.
 """
+
+# -----------------------------------------------------------------------------
+# Level 3 AAC sequence payload types (Quantizer + Huffman)
+# -----------------------------------------------------------------------------
+
+class AACChannelFrameF3(TypedDict):
+    """
+    Per-channel payload for aac_seq_3[i]["chl"] or ["chr"] (Level 3).
+
+    Keys
+    ----
+    tns_coeffs:
+        Quantized TNS predictor coefficients for ONE channel.
+        Shapes:
+        - ESH: (PRED_ORDER, 8)
+        - else: (PRED_ORDER, 1)
+
+    T:
+        Psychoacoustic thresholds per band.
+        Shapes:
+        - ESH: (NB, 8)
+        - else: (NB, 1)
+        Note: Stored for completeness / debugging; not entropy-coded.
+
+    G:
+        Quantized global gains.
+        Shapes:
+        - ESH: (1, 8)  (one per short subframe)
+        - else: scalar (or compatible np scalar)
+
+    sfc:
+        Huffman-coded scalefactor differences (DPCM sequence).
+
+    stream:
+        Huffman-coded MDCT quantized symbols S(k) (packed to 1024 symbols).
+
+    codebook:
+        Huffman codebook id used for MDCT symbols (stream).
+        (Scalefactors typically use fixed codebook 11 and do not need to store it.)
+    """
+    tns_coeffs: TnsCoeffs
+    T: FloatArray
+    G: FloatArray | float
+    sfc: HuffmanBitstream
+    stream: HuffmanBitstream
+    codebook: HuffmanCodebook
+
+
+class AACSeq3Frame(TypedDict):
+    """
+    One frame dictionary element of aac_seq_3 (Level 3).
+    """
+    frame_type: FrameType
+    win_type: WinType
+    chl: AACChannelFrameF3
+    chr: AACChannelFrameF3
+
+
+AACSeq3: TypeAlias = List[AACSeq3Frame]
+"""
+AAC sequence for Level 3:
+List of length K (K = number of frames).
+
+Each element is a dict with keys:
+- "frame_type", "win_type", "chl", "chr"
+
+Level 3 adds (per channel):
+- "tns_coeffs"
+- "T" thresholds (not entropy-coded)
+- "G" global gain(s)
+- "sfc" Huffman-coded scalefactor differences
+- "stream" Huffman-coded MDCT quantized symbols
+- "codebook" Huffman codebook for MDCT symbols
+"""

source/core/tests/test_aac_coder_decoder.py

@@ -19,10 +19,10 @@ import numpy as np
 import pytest
 import soundfile as sf
 
-from core.aac_coder import aac_coder_1, aac_coder_2, aac_read_wav_stereo_48k
+from core.aac_coder import aac_coder_1, aac_coder_2, aac_coder_3, aac_read_wav_stereo_48k
-from core.aac_decoder import aac_decoder_1, aac_decoder_2, aac_remove_padding
+from core.aac_decoder import aac_decoder_1, aac_decoder_2, aac_decoder_3, aac_remove_padding
-from core.aac_types import *
 from core.aac_utils import snr_db
+from core.aac_types import *
 
 
 # Helper "fixtures" for aac_coder_1 / i_aac_coder_1
@@ -223,3 +223,152 @@ def test_end_to_end_level_2_high_snr(tmp_stereo_wav: Path, tmp_path: Path) -> No
 
     snr = snr_db(x_ref, x_hat)
     assert snr > 80
+
+
+# -----------------------------------------------------------------------------
+# Level 3 tests (Quantizer + Huffman)
+# -----------------------------------------------------------------------------
+
+@pytest.fixture(scope="module")
+def wav_in_path() -> Path:
+    """
+    Input WAV used for end-to-end tests.
+
+    This should point to the provided test audio under material/.
+    Adjust this path if your project layout differs.
+    """
+    # Typical layout in this project:
+    # source/material/LicorDeCalandraca.wav
+    return Path(__file__).resolve().parents[2] / "material" / "LicorDeCalandraca.wav"
+
+
+def _assert_level3_frame_schema(frame: AACSeq3Frame) -> None:
+    """
+    Validate Level-3 per-frame schema (keys + basic types only).
+    """
+    assert "frame_type" in frame
+    assert "win_type" in frame
+    assert "chl" in frame
+    assert "chr" in frame
+
+    for ch_key in ("chl", "chr"):
+        ch = frame[ch_key]  # type: ignore[index]
+        assert "tns_coeffs" in ch
+        assert "T" in ch
+        assert "G" in ch
+        assert "sfc" in ch
+        assert "stream" in ch
+        assert "codebook" in ch
+
+        assert isinstance(ch["sfc"], str)
+        assert isinstance(ch["stream"], str)
+        assert isinstance(ch["codebook"], int)
+
+        # Arrays: only check they are numpy arrays with expected dtype categories.
+        assert isinstance(ch["tns_coeffs"], np.ndarray)
+        assert isinstance(ch["T"], np.ndarray)
+
+        # Global gain: long frames may be scalar float, ESH may be ndarray
+        assert np.isscalar(ch["G"]) or isinstance(ch["G"], np.ndarray)
+
+
+def test_aac_coder_3_seq_schema_and_shapes(wav_in_path: Path, tmp_path: Path) -> None:
+    """
+    Contract test:
+    - aac_coder_3 returns AACSeq3
+    - Per-frame keys exist and types are consistent
+    - Basic shape expectations hold for ESH vs non-ESH cases
+
+    Note:
+    This test uses a short excerpt (a few frames) to keep runtime bounded.
+    """
+    # Use only a few frames to avoid long runtimes in the quantizer loop.
+    hop = 1024
+    win = 2048
+    n_frames = 4
+    n_samples = win + (n_frames - 1) * hop
+
+    x, fs = aac_read_wav_stereo_48k(wav_in_path)
+    x_short = x[:n_samples, :]
+
+    short_wav = tmp_path / "input_short.wav"
+    sf.write(str(short_wav), x_short, fs)
+
+    aac_seq_3: AACSeq3 = aac_coder_3(short_wav)
+
+    assert isinstance(aac_seq_3, list)
+    assert len(aac_seq_3) > 0
+
+    for fr in aac_seq_3:
+        _assert_level3_frame_schema(fr)
+
+        frame_type = fr["frame_type"]
+        for ch_key in ("chl", "chr"):
+            ch = fr[ch_key]  # type: ignore[index]
+
+            tns = np.asarray(ch["tns_coeffs"])
+            if frame_type == "ESH":
+                assert tns.ndim == 2
+                assert tns.shape[1] == 8
+            else:
+                assert tns.ndim == 2
+                assert tns.shape[1] == 1
+
+            T = np.asarray(ch["T"])
+            if frame_type == "ESH":
+                assert T.ndim == 2
+                assert T.shape[1] == 8
+            else:
+                assert T.ndim == 2
+                assert T.shape[1] == 1
+
+            G = ch["G"]
+            if frame_type == "ESH":
+                assert isinstance(G, np.ndarray)
+                assert np.asarray(G).shape == (1, 8)
+            else:
+                assert np.isscalar(G)
+
+            assert isinstance(ch["sfc"], str)
+            assert isinstance(ch["stream"], str)
+
+
+
+def test_end_to_end_level_3_high_snr(wav_in_path: Path, tmp_path: Path) -> None:
+    """
+    End-to-end test for Level 3 (Quantizer + Huffman):
+
+    coder_3 -> decoder_3 should reconstruct a waveform with acceptable SNR.
+
+    Notes
+    -----
+    - Level 3 includes quantization, so SNR is expected to be lower than Level 1/2.
+    - We intentionally use a short excerpt (few frames) to keep runtime bounded,
+      since the reference quantizer implementation is computationally expensive.
+    """
+    # Use only a few frames to avoid long runtimes.
+    hop = 1024
+    win = 2048
+    n_frames = 4
+    n_samples = win + (n_frames - 1) * hop
+
+    x_ref, fs = aac_read_wav_stereo_48k(wav_in_path)
+    x_short = x_ref[:n_samples, :]
+
+    short_wav = tmp_path / "input_short_l3.wav"
+    sf.write(str(short_wav), x_short, fs)
+
+    out_wav = tmp_path / "decoded_level3.wav"
+
+    aac_seq_3: AACSeq3 = aac_coder_3(short_wav)
+    y_hat: StereoSignal = aac_decoder_3(aac_seq_3, out_wav)
+
+    # Align lengths defensively (padding removal may differ by a few samples)
+    n = min(x_short.shape[0], y_hat.shape[0])
+    x2 = x_short[:n, :]
+    y2 = y_hat[:n, :]
+
+    s = snr_db(x2, y2)
+
+    # Conservative threshold: Level 3 is lossy by design.
+    assert s > 10.0

source/core/tests/test_huffman.py

@@ -0,0 +1,139 @@
+# ------------------------------------------------------------
+# AAC Coder/Decoder - Huffman Wrapper Tests (Level 3)
+#
+# Multimedia course at Aristotle University of
+# Thessaloniki (AUTh)
+#
+# Author:
+#   Christos Choutouridis (ΑΕΜ 8997)
+#   cchoutou@ece.auth.gr
+#
+# Description:
+#   Contract tests for the Huffman coding stage, using the provided
+#   Huffman utilities (material/huff_utils.py).
+#
+#   The Huffman encoder/decoder itself is GIVEN by the assignment and
+#   is not re-implemented here. These tests only verify that:
+#
+#   - The wrapper functions (aac_encode_huff / aac_decode_huff) expose
+#     the API described in the assignment.
+#   - Forced codebook selection works as expected (e.g. scalefactors).
+#   - Tuple-based Huffman coding semantics are respected.
+#
+# Notes on tuple coding:
+#   Huffman coding operates on tuples of symbols. As a result,
+#   decode(encode(x)) may return extra trailing symbols due to padding.
+#   The AAC decoder always knows the true section length (from band limits)
+#   and truncates accordingly. Therefore, these tests only enforce that
+#   the decoded PREFIX matches the original data.
+# ------------------------------------------------------------
+from __future__ import annotations
+
+import numpy as np
+import pytest
+
+from core.aac_huffman import aac_encode_huff, aac_decode_huff
+from material.huff_utils import load_LUT
+
+
+# -----------------------------------------------------------------------------
+# Fixtures
+# -----------------------------------------------------------------------------
+
+@pytest.fixture(scope="module")
+def huff_LUT():
+    """
+    Load Huffman Look-Up Tables (LUTs) once per test module.
+
+    The LUTs are provided by the assignment (huffCodebooks.mat) via
+    material.huff_utils.load_LUT().
+    """
+    return load_LUT()
+
+
+# -----------------------------------------------------------------------------
+# Roundtrip (prefix) tests
+# -----------------------------------------------------------------------------
+
+@pytest.mark.parametrize(
+    "coeff_sec",
+    [
+        np.array([1, -1, 2, -2, 0, 0, 3], dtype=np.int64),
+        np.array([0, 0, 0, 0], dtype=np.int64),
+        np.array([5], dtype=np.int64),
+        np.array([-3, -3, -3, -3], dtype=np.int64),
+    ],
+)
+def test_huffman_roundtrip_prefix_matches(
+    coeff_sec: np.ndarray,
+    huff_LUT,
+) -> None:
+    """
+    Contract test for Huffman encode/decode.
+
+    Guarantees:
+    - Encoding followed by decoding does not crash.
+    - The decoded output has at least as many symbols as the input.
+    - The prefix of the decoded output matches the original coefficients.
+
+    Rationale:
+    Huffman tuple coding may introduce padding, so exact length equality
+    is NOT required or expected.
+    """
+    huff_sec, cb = aac_encode_huff(coeff_sec, huff_LUT)
+    dec = aac_decode_huff(huff_sec, cb, huff_LUT)
+
+    if cb == 0:
+        # Codebook 0 represents an all-zero section.
+        assert np.all(coeff_sec == 0)
+        assert dec.size == 0
+        return
+
+    assert dec.size >= coeff_sec.size
+    np.testing.assert_array_equal(dec[: coeff_sec.size], coeff_sec)
+
+
+# -----------------------------------------------------------------------------
+# Forced codebook tests
+# -----------------------------------------------------------------------------
+
+def test_huffman_force_codebook_returns_requested_codebook(huff_LUT) -> None:
+    """
+    Verify forced codebook selection.
+
+    According to the assignment, scalefactors must be encoded using
+    Huffman codebook 11. This test checks that:
+    - The requested codebook is actually used.
+    - The decoded prefix matches the original scalefactors.
+    """
+    scalefactors = np.array([10, -2, 1, 0, -1, 3], dtype=np.int64)
+
+    huff_sec, cb = aac_encode_huff(
+        scalefactors,
+        huff_LUT,
+        force_codebook=11,
+    )
+
+    assert cb == 11
+    assert isinstance(huff_sec, str)
+
+    dec = aac_decode_huff(huff_sec, cb, huff_LUT)
+
+    assert dec.size >= scalefactors.size
+    np.testing.assert_array_equal(dec[: scalefactors.size], scalefactors)
+
+
+# -----------------------------------------------------------------------------
+# Error handling
+# -----------------------------------------------------------------------------
+
+def test_huffman_invalid_codebook_raises(huff_LUT) -> None:
+    """
+    Decoding with an invalid Huffman codebook index must raise an error.
+    """
+    with pytest.raises(Exception):
+        _ = aac_decode_huff(
+            huff_sec="010101",
+            huff_codebook=99,
+            huff_LUT=huff_LUT,
+        )

source/core/tests/test_quantizer.py

@@ -0,0 +1,395 @@
+# ------------------------------------------------------------
+# AAC Coder/Decoder - Quantizer Tests
+#
+# Multimedia course at Aristotle University of
+# Thessaloniki (AUTh)
+#
+# Author:
+#   Christos Choutouridis (ΑΕΜ 8997)
+#   cchoutou@ece.auth.gr
+#
+# Description:
+#   Tests for Quantizer / iQuantizer module.
+#
+#   These tests are deliberately "contract-oriented":
+#   - They validate shapes, dtypes and invariants that downstream stages
+#     (e.g., Huffman coding) depend on.
+#   - They do not attempt to validate psychoacoustic optimality (that would
+#     require a reference implementation and careful numerical baselines).
+#
+# Validates:
+#   - I/O shapes for long and ESH modes
+#   - DPCM scalefactor coding consistency (sfc)
+#   - ESH packing order of quantized symbols (128x8 <-> 1024)
+#   - Edge cases (zeros / near silence)
+#   - Sanity (finite outputs, no extreme numerical blow-up)
+# ------------------------------------------------------------
+from __future__ import annotations
+
+import numpy as np
+import pytest
+
+from core.aac_quantizer import aac_quantizer, aac_i_quantizer
+from core.aac_utils import get_table, band_limits
+from core.aac_types import FrameType
+
+
+# Small epsilon to avoid divisions by zero in sanity ratios
+EPS = 1e-12
+
+
+# -----------------------------------------------------------------------------
+# Helper utilities
+# -----------------------------------------------------------------------------
+
+def _nbands(frame_type: FrameType) -> int:
+    """
+    Return number of scalefactor bands for the given frame type.
+
+    This is derived from TableB219 (psycho tables) via aac_utils helpers,
+    so the tests remain consistent even if tables are updated.
+    """
+    table, _nfft = get_table(frame_type)
+    wlow, _whigh, _bval, _qthr = band_limits(table)
+    return int(len(wlow))
+
+
+def _make_smr(frame_type: FrameType, seed: int = 0) -> np.ndarray:
+    """
+    Create a strictly positive SMR array with the correct shape.
+
+    These tests are not about psycho correctness; they only need SMR > 0
+    to avoid division by zero and to make the quantizer's threshold logic
+    behave deterministically.
+    """
+    rng = np.random.default_rng(seed)
+    NB = _nbands(frame_type)
+
+    if frame_type == "ESH":
+        # ESH uses 8 short windows, thus SMR has 8 columns.
+        return (1.0 + np.abs(rng.normal(size=(NB, 8)))).astype(np.float64)
+
+    # Long frames: use a column vector (NB, 1).
+    return (1.0 + np.abs(rng.normal(size=(NB, 1)))).astype(np.float64)
+
+
+def _reconstruct_alpha_from_sfc(sfc: np.ndarray) -> np.ndarray:
+    """
+    Reconstruct alpha(b) from DPCM-coded scalefactors sfc(b).
+
+    By definition in the assignment:
+        sfc(0) = alpha(0)
+        alpha(b) = alpha(b-1) + sfc(b)  for b > 0
+
+    This reconstruction is useful to validate the internal consistency
+    of the produced scalefactor information.
+    """
+    sfc = np.asarray(sfc, dtype=np.int64)
+
+    # Long frames: sfc shape (NB, 1)
+    if sfc.ndim == 2 and sfc.shape[1] == 1:
+        NB = sfc.shape[0]
+        alpha = np.zeros((NB,), dtype=np.int64)
+        alpha[0] = int(sfc[0, 0])
+        for b in range(1, NB):
+            alpha[b] = int(alpha[b - 1] + sfc[b, 0])
+        return alpha
+
+    # ESH frames: sfc shape (NB, 8)
+    if sfc.ndim == 2 and sfc.shape[1] == 8:
+        NB = sfc.shape[0]
+        alpha = np.zeros((NB, 8), dtype=np.int64)
+        alpha[0, :] = sfc[0, :]
+        for b in range(1, NB):
+            alpha[b, :] = alpha[b - 1, :] + sfc[b, :]
+        return alpha
+
+    raise ValueError("Unsupported sfc shape.")
+
+
+# -----------------------------------------------------------------------------
+# Shape / contract tests
+# -----------------------------------------------------------------------------
+
+@pytest.mark.parametrize("frame_type", ["OLS", "LSS", "LPS"])
+def test_quantizer_shapes_long(frame_type: FrameType) -> None:
+    """
+    Contract test for long frames:
+    - Input: MDCT coefficients shape (1024, 1)
+    - Output S: always (1024, 1)
+    - Output sfc: (NB, 1)
+    - G: scalar float for long frames
+    - iQuantizer output: (1024, 1)
+    """
+    NB = _nbands(frame_type)
+    rng = np.random.default_rng(1)
+
+    X = rng.normal(size=(1024, 1)).astype(np.float64)
+    SMR = _make_smr(frame_type, seed=2)
+
+    S, sfc, G = aac_quantizer(X, frame_type, SMR)
+
+    assert S.shape == (1024, 1)
+    assert sfc.shape == (NB, 1)
+    assert isinstance(G, (float, np.floating))
+
+    Xhat = aac_i_quantizer(S, sfc, G, frame_type)
+    assert Xhat.shape == (1024, 1)
+
+
+def test_quantizer_shapes_esh() -> None:
+    """
+    Contract test for ESH frames:
+    - Input: MDCT coefficients shape (128, 8)
+    - Output S: packed to (1024, 1)
+    - Output sfc: (NB, 8)
+    - G: array shape (1, 8) for ESH (one gain per short window)
+    - iQuantizer output: (128, 8)
+    """
+    frame_type: FrameType = "ESH"
+    NB = _nbands(frame_type)
+    rng = np.random.default_rng(3)
+
+    X = rng.normal(size=(128, 8)).astype(np.float64)
+    SMR = _make_smr(frame_type, seed=4)
+
+    S, sfc, G = aac_quantizer(X, frame_type, SMR)
+
+    assert S.shape == (1024, 1)
+    assert sfc.shape == (NB, 8)
+    assert isinstance(G, np.ndarray)
+    assert G.shape == (1, 8)
+
+    Xhat = aac_i_quantizer(S, sfc, G, frame_type)
+    assert Xhat.shape == (128, 8)
+
+
+# -----------------------------------------------------------------------------
+# DPCM consistency tests
+# -----------------------------------------------------------------------------
+
+@pytest.mark.parametrize("frame_type", ["OLS", "LSS", "LPS"])
+def test_quantizer_dpcm_reconstructs_alpha_long(frame_type: FrameType) -> None:
+    """
+    Verify the DPCM coding rule for long frames.
+
+    The quantizer returns:
+      sfc(0) = alpha(0)
+      sfc(b) = alpha(b) - alpha(b-1), b>0
+
+    Reconstruct alpha from sfc and check:
+      alpha(0) == sfc(0) == G
+    """
+    rng = np.random.default_rng(5)
+
+    X = rng.normal(size=(1024, 1)).astype(np.float64)
+    SMR = _make_smr(frame_type, seed=6)
+
+    _S, sfc, G = aac_quantizer(X, frame_type, SMR)
+
+    alpha = _reconstruct_alpha_from_sfc(sfc)
+
+    assert int(sfc[0, 0]) == int(alpha[0])
+    assert float(alpha[0]) == float(G)
+
+
+def test_quantizer_dpcm_reconstructs_alpha_esh() -> None:
+    """
+    Verify the DPCM coding rule for ESH frames.
+
+    For each short window j:
+      sfc(0, j) = alpha(0, j) == G(0, j)
+    """
+    frame_type: FrameType = "ESH"
+    rng = np.random.default_rng(7)
+
+    X = rng.normal(size=(128, 8)).astype(np.float64)
+    SMR = _make_smr(frame_type, seed=8)
+
+    _S, sfc, G = aac_quantizer(X, frame_type, SMR)
+
+    alpha = _reconstruct_alpha_from_sfc(sfc)
+
+    assert np.all(alpha[0, :] == sfc[0, :])
+    assert np.all(alpha[0, :] == G.reshape(-1))
+
+
+# -----------------------------------------------------------------------------
+# ESH packing order test
+# -----------------------------------------------------------------------------
+
+def test_quantizer_esh_packing_order_matches_iquantizer_layout() -> None:
+    """
+    Verify ESH packing order.
+
+    The quantizer outputs S in packed shape (1024, 1). The expected packing
+    is column-major concatenation of the 8 short subframes.
+
+    This test constructs a deterministic input where each subframe column
+    has a distinct constant value. After quantize+inverse-quantize, the
+    reconstructed columns should remain distinguishable in the same order.
+
+    This primarily tests ordering, not exact numerical values.
+    """
+    frame_type: FrameType = "ESH"
+    NB = _nbands(frame_type)
+
+    # Create 8 distinct subframes: column j is constant (j+1)
+    X = np.zeros((128, 8), dtype=np.float64)
+    for j in range(8):
+        X[:, j] = float(j + 1)
+
+    # Use very large SMR so thresholds are permissive and alpha changes are
+    # minimal. This helps keep the ordering signal strong.
+    SMR = np.ones((NB, 8), dtype=np.float64) * 1e6
+
+    S, sfc, G = aac_quantizer(X, frame_type, SMR)
+    Xhat = aac_i_quantizer(S, sfc, G, frame_type)
+
+    # The average magnitude per column must be increasing with the original order.
+    col_means = np.mean(Xhat, axis=0)
+    assert np.all(np.diff(col_means) > 0.0)
+
+
+# -----------------------------------------------------------------------------
+# Edge cases: zeros and near-silence
+# -----------------------------------------------------------------------------
+
+@pytest.mark.parametrize("frame_type", ["OLS", "LSS", "LPS"])
+def test_quantizer_zero_input_long_is_finite(frame_type: FrameType) -> None:
+    """
+    Edge case: zero MDCT coefficients should not produce NaN/Inf.
+
+    We do not require identity here (quantizer is lossy), but we require
+    the pipeline to remain numerically safe and produce finite outputs.
+    """
+    NB = _nbands(frame_type)
+
+    X = np.zeros((1024, 1), dtype=np.float64)
+    SMR = np.ones((NB, 1), dtype=np.float64)
+
+    S, sfc, G = aac_quantizer(X, frame_type, SMR)
+    assert np.isfinite(S).all()
+    assert np.isfinite(sfc).all()
+    assert isinstance(G, (float, np.floating))
+
+    Xhat = aac_i_quantizer(S, sfc, G, frame_type)
+    assert np.isfinite(Xhat).all()
+
+
+def test_quantizer_zero_input_esh_is_finite() -> None:
+    """
+    Edge case: same as above, for ESH mode.
+    """
+    frame_type: FrameType = "ESH"
+    NB = _nbands(frame_type)
+
+    X = np.zeros((128, 8), dtype=np.float64)
+    SMR = np.ones((NB, 8), dtype=np.float64)
+
+    S, sfc, G = aac_quantizer(X, frame_type, SMR)
+    assert np.isfinite(S).all()
+    assert np.isfinite(sfc).all()
+    assert np.isfinite(G).all()
+
+    Xhat = aac_i_quantizer(S, sfc, G, frame_type)
+    assert np.isfinite(Xhat).all()
+
+
+@pytest.mark.parametrize("frame_type", ["OLS", "LSS", "LPS"])
+def test_quantizer_near_silence_long_is_finite(frame_type: FrameType) -> None:
+    """
+    Edge case: extremely small values.
+
+    This stresses numerical guards (EPS usage) and ensures no invalid operations.
+    """
+    NB = _nbands(frame_type)
+
+    X = (1e-15 * np.ones((1024, 1), dtype=np.float64))
+    SMR = np.ones((NB, 1), dtype=np.float64)
+
+    S, sfc, G = aac_quantizer(X, frame_type, SMR)
+    assert np.isfinite(S).all()
+    assert np.isfinite(sfc).all()
+
+    Xhat = aac_i_quantizer(S, sfc, G, frame_type)
+    assert np.isfinite(Xhat).all()
+
+
+def test_quantizer_near_silence_esh_is_finite() -> None:
+    """
+    Edge case: extremely small values, ESH mode.
+    """
+    frame_type: FrameType = "ESH"
+    NB = _nbands(frame_type)
+
+    X = (1e-15 * np.ones((128, 8), dtype=np.float64))
+    SMR = np.ones((NB, 8), dtype=np.float64)
+
+    S, sfc, G = aac_quantizer(X, frame_type, SMR)
+    assert np.isfinite(S).all()
+    assert np.isfinite(sfc).all()
+    assert np.isfinite(G).all()
+
+    Xhat = aac_i_quantizer(S, sfc, G, frame_type)
+    assert np.isfinite(Xhat).all()
+
+
+# -----------------------------------------------------------------------------
+# Sanity: avoid catastrophic numerical blow-up
+# -----------------------------------------------------------------------------
+
+@pytest.mark.parametrize("frame_type", ["OLS", "LSS", "LPS"])
+def test_quantizer_sanity_no_extreme_blowup_long(frame_type: FrameType) -> None:
+    """
+    Loose sanity guard.
+
+    The quantizer is lossy, but it should not produce reconstructions with
+    catastrophic peak/energy growth compared to the input.
+    """
+    NB = _nbands(frame_type)
+    rng = np.random.default_rng(11)
+
+    X = rng.normal(size=(1024, 1)).astype(np.float64)
+    SMR = np.ones((NB, 1), dtype=np.float64) * 10.0
+
+    S, sfc, G = aac_quantizer(X, frame_type, SMR)
+    Xhat = aac_i_quantizer(S, sfc, G, frame_type)
+
+    in_peak = float(np.max(np.abs(X)))
+    out_peak = float(np.max(np.abs(Xhat)))
+    peak_ratio = out_peak / (in_peak + EPS)
+
+    in_energy = float(np.sum(X * X))
+    out_energy = float(np.sum(Xhat * Xhat))
+    energy_ratio = out_energy / (in_energy + EPS)
+
+    # Very loose thresholds: only catch severe regressions.
+    assert peak_ratio < 100.0
+    assert energy_ratio < 1e4
+
+
+def test_quantizer_sanity_no_extreme_blowup_esh() -> None:
+    """
+    Same loose sanity guard for ESH mode.
+    """
+    frame_type: FrameType = "ESH"
+    NB = _nbands(frame_type)
+    rng = np.random.default_rng(12)
+
+    X = rng.normal(size=(128, 8)).astype(np.float64)
+    SMR = np.ones((NB, 8), dtype=np.float64) * 10.0
+
+    S, sfc, G = aac_quantizer(X, frame_type, SMR)
+    Xhat = aac_i_quantizer(S, sfc, G, frame_type)
+
+    in_peak = float(np.max(np.abs(X)))
+    out_peak = float(np.max(np.abs(Xhat)))
+    peak_ratio = out_peak / (in_peak + EPS)
+
+    in_energy = float(np.sum(X * X))
+    out_energy = float(np.sum(Xhat * Xhat))
+    energy_ratio = out_energy / (in_energy + EPS)
+
+    assert peak_ratio < 100.0
+    assert energy_ratio < 1e4

source/core/tests/test_ssc.py

@@ -16,7 +16,7 @@ from __future__ import annotations
 
 import numpy as np
 
-from core.aac_ssc import aac_SSC
+from core.aac_ssc import aac_ssc
 from core.aac_types import FrameT
 
 # -----------------------------------------------------------------------------
@@ -117,10 +117,10 @@ def test_ssc_fixed_cases_prev_lss_and_lps() -> None:
 
     next_attack = _next_frame_strong_attack(attack_left=True, attack_right=True)
 
-    out1 = aac_SSC(frame_t, next_attack, "LSS")
+    out1 = aac_ssc(frame_t, next_attack, "LSS")
     assert out1 == "ESH"
 
-    out2 = aac_SSC(frame_t, next_attack, "LPS")
+    out2 = aac_ssc(frame_t, next_attack, "LPS")
     assert out2 == "OLS"
 
 
@@ -138,7 +138,7 @@ def test_prev_ols_next_not_esh_returns_ols() -> None:
     frame_t: FrameT = np.zeros((2048, 2), dtype=np.float64)
     next_t = _next_frame_no_attack()
 
-    out = aac_SSC(frame_t, next_t, "OLS")
+    out = aac_ssc(frame_t, next_t, "OLS")
     assert out == "OLS"
 
 
@@ -151,7 +151,7 @@ def test_prev_ols_next_esh_both_channels_returns_lss() -> None:
     frame_t: FrameT = np.zeros((2048, 2), dtype=np.float64)
     next_t = _next_frame_strong_attack(attack_left=True, attack_right=True)
 
-    out = aac_SSC(frame_t, next_t, "OLS")
+    out = aac_ssc(frame_t, next_t, "OLS")
     assert out == "LSS"
 
 
@@ -165,11 +165,11 @@ def test_prev_ols_next_esh_one_channel_returns_lss() -> None:
     frame_t: FrameT = np.zeros((2048, 2), dtype=np.float64)
 
     next1_t = _next_frame_strong_attack(attack_left=True, attack_right=False)
-    out1 = aac_SSC(frame_t, next1_t, "OLS")
+    out1 = aac_ssc(frame_t, next1_t, "OLS")
     assert out1 == "LSS"
 
     next2_t = _next_frame_strong_attack(attack_left=False, attack_right=True)
-    out2 = aac_SSC(frame_t, next2_t, "OLS")
+    out2 = aac_ssc(frame_t, next2_t, "OLS")
     assert out2 == "LSS"
 
 
@@ -182,7 +182,7 @@ def test_prev_esh_next_esh_both_channels_returns_esh() -> None:
     frame_t: FrameT = np.zeros((2048, 2), dtype=np.float64)
     next_t = _next_frame_strong_attack(attack_left=True, attack_right=True)
 
-    out = aac_SSC(frame_t, next_t, "ESH")
+    out = aac_ssc(frame_t, next_t, "ESH")
     assert out == "ESH"
 
 
@@ -195,7 +195,7 @@ def test_prev_esh_next_not_esh_both_channels_returns_lps() -> None:
     frame_t: FrameT = np.zeros((2048, 2), dtype=np.float64)
     next_t = _next_frame_no_attack()
 
-    out = aac_SSC(frame_t, next_t, "ESH")
+    out = aac_ssc(frame_t, next_t, "ESH")
     assert out == "LPS"
 
 
@@ -209,11 +209,11 @@ def test_prev_esh_next_esh_one_channel_merged_is_esh() -> None:
     frame_t: FrameT = np.zeros((2048, 2), dtype=np.float64)
 
     next1_t = _next_frame_strong_attack(attack_left=True, attack_right=False)
-    out1 = aac_SSC(frame_t, next1_t, "ESH")
+    out1 = aac_ssc(frame_t, next1_t, "ESH")
     assert out1 == "ESH"
 
     next2_t = _next_frame_strong_attack(attack_left=False, attack_right=True)
-    out2 = aac_SSC(frame_t, next2_t, "ESH")
+    out2 = aac_ssc(frame_t, next2_t, "ESH")
     assert out2 == "ESH"
 
 
@@ -230,5 +230,5 @@ def test_threshold_s_must_exceed_1e_3() -> None:
     frame_t: FrameT = np.zeros((2048, 2), dtype=np.float64)
     next_t = _next_frame_below_s_threshold(left=True, right=True, impulse_amp=0.01)
 
-    out = aac_SSC(frame_t, next_t, "OLS")
+    out = aac_ssc(frame_t, next_t, "OLS")
     assert out == "OLS"

source/core/tests/test_tns.py

@@ -26,6 +26,7 @@ from core.aac_configuration import PRED_ORDER, QUANT_MAX, QUANT_STEP
 from core.aac_tns import aac_tns, aac_i_tns
 from core.aac_types import *
 
+EPS = 1e-12
 
 # -----------------------------------------------------------------------------
 # Helper utilities
@@ -194,3 +195,132 @@ def test_tns_outputs_are_finite() -> None:
     out_esh, coeffs_esh = aac_tns(frame_F_esh, "ESH")
     assert np.isfinite(out_esh).all()
     assert np.isfinite(coeffs_esh).all()
+
+
+@pytest.mark.parametrize("frame_type", ["OLS", "LSS", "LPS"])
+def test_tns_zero_input_is_identity_long(frame_type: FrameType) -> None:
+    """
+    Edge case: zero MDCT coefficients should remain zero after TNS and iTNS.
+    This checks that no NaN/Inf appears and the pipeline is numerically safe.
+    """
+    frame_F_in = np.zeros((1024, 1), dtype=np.float64)
+
+    frame_F_tns, tns_coeffs = aac_tns(frame_F_in, frame_type)
+    assert np.isfinite(frame_F_tns).all()
+    assert np.isfinite(tns_coeffs).all()
+    assert np.all(frame_F_tns == 0.0)
+
+    frame_F_hat = aac_i_tns(frame_F_tns, frame_type, tns_coeffs)
+    assert np.isfinite(frame_F_hat).all()
+    assert np.all(frame_F_hat == 0.0)
+
+
+def test_tns_zero_input_is_identity_esh() -> None:
+    """
+    Edge case: zero MDCT coefficients should remain zero for ESH too.
+    """
+    frame_F_in = np.zeros((128, 8), dtype=np.float64)
+
+    frame_F_tns, tns_coeffs = aac_tns(frame_F_in, "ESH")
+    assert np.isfinite(frame_F_tns).all()
+    assert np.isfinite(tns_coeffs).all()
+    assert np.all(frame_F_tns == 0.0)
+
+    frame_F_hat = aac_i_tns(frame_F_tns, "ESH", tns_coeffs)
+    assert np.isfinite(frame_F_hat).all()
+    assert np.all(frame_F_hat == 0.0)
+
+
+@pytest.mark.parametrize("frame_type", ["OLS", "LSS", "LPS"])
+def test_tns_near_silence_is_finite_and_roundtrips(frame_type: FrameType) -> None:
+    """
+    Edge case: extremely small values should not cause NaN/Inf,
+    and round-trip should remain close.
+    """
+    frame_F_in = (1e-15 * np.ones((1024, 1), dtype=np.float64))
+
+    frame_F_tns, tns_coeffs = aac_tns(frame_F_in, frame_type)
+    assert np.isfinite(frame_F_tns).all()
+    assert np.isfinite(tns_coeffs).all()
+
+    frame_F_hat = aac_i_tns(frame_F_tns, frame_type, tns_coeffs)
+    assert np.isfinite(frame_F_hat).all()
+
+    np.testing.assert_allclose(frame_F_hat, frame_F_in, rtol=1e-6, atol=1e-12)
+
+
+def test_tns_near_silence_esh_is_finite_and_roundtrips() -> None:
+    """
+    Near-silence test for ESH mode.
+    """
+    frame_F_in = (1e-15 * np.ones((128, 8), dtype=np.float64))
+
+    frame_F_tns, tns_coeffs = aac_tns(frame_F_in, "ESH")
+    assert np.isfinite(frame_F_tns).all()
+    assert np.isfinite(tns_coeffs).all()
+
+    frame_F_hat = aac_i_tns(frame_F_tns, "ESH", tns_coeffs)
+    assert np.isfinite(frame_F_hat).all()
+
+    np.testing.assert_allclose(frame_F_hat, frame_F_in, rtol=1e-6, atol=1e-12)
+
+
+@pytest.mark.parametrize("frame_type", ["OLS", "LSS", "LPS"])
+def test_tns_accepts_flat_vector_shape_long(frame_type: FrameType) -> None:
+    """
+    Contract test: for non-ESH, aac_tns must accept input shape (1024,)
+    in addition to (1024, 1), and preserve the shape convention.
+    """
+    rng = np.random.default_rng(7)
+    frame_F_in = rng.normal(size=(1024,)).astype(np.float64)
+
+    frame_F_out, tns_coeffs = aac_tns(frame_F_in, frame_type)
+
+    assert frame_F_out.shape == (1024,)
+    assert tns_coeffs.shape == (PRED_ORDER, 1)
+
+
+@pytest.mark.parametrize("frame_type", ["OLS", "LSS", "LPS"])
+def test_tns_does_not_explode_peak_or_energy_long(frame_type: FrameType) -> None:
+    """
+    Sanity: TNS should not cause extreme peak/energy blow-up on typical inputs.
+    This is a loose guard to catch regressions.
+    """
+    rng = np.random.default_rng(8)
+    frame_F_in = rng.normal(size=(1024, 1)).astype(np.float64)
+
+    in_peak = float(np.max(np.abs(frame_F_in)))
+    in_energy = float(np.sum(frame_F_in * frame_F_in))
+
+    frame_F_out, _ = aac_tns(frame_F_in, frame_type)
+
+    out_peak = float(np.max(np.abs(frame_F_out)))
+    out_energy = float(np.sum(frame_F_out * frame_F_out))
+
+    peak_ratio = out_peak / (in_peak + EPS)
+    energy_ratio = out_energy / (in_energy + EPS)
+
+    assert peak_ratio < 50.0
+    assert energy_ratio < 2500.0
+
+
+def test_tns_does_not_explode_peak_or_energy_esh() -> None:
+    """
+    Sanity: same blow-up guard for ESH mode.
+    """
+    rng = np.random.default_rng(9)
+    frame_F_in = rng.normal(size=(128, 8)).astype(np.float64)
+
+    in_peak = float(np.max(np.abs(frame_F_in)))
+    in_energy = float(np.sum(frame_F_in * frame_F_in))
+
+    frame_F_out, _ = aac_tns(frame_F_in, "ESH")
+
+    out_peak = float(np.max(np.abs(frame_F_out)))
+    out_energy = float(np.sum(frame_F_out * frame_F_out))
+
+    peak_ratio = out_peak / (in_peak + EPS)
+    energy_ratio = out_energy / (in_energy + EPS)
+
+    assert peak_ratio < 50.0
+    assert energy_ratio < 2500.0

source/level_1/core/aac_coder.py

@@ -9,8 +9,16 @@
 #   cchoutou@ece.auth.gr
 #
 # Description:
-#   - Level 1 AAC encoder orchestration.
+#   Level 1 AAC encoder orchestration.
-#   - Level 2 AAC encoder orchestration.
+#   Keeps the same functional behavior as the original level_1 implementation:
+#   - Reads WAV via soundfile
+#   - Validates stereo and 48 kHz
+#   - Frames into 2048 samples with hop=1024 and zero padding at both ends
+#   - SSC decision uses next-frame attack detection
+#   - Filterbank analysis (MDCT)
+#   - Stores per-channel spectra in AACSeq1 schema:
+#       * ESH: (128, 8)
+#       * else: (1024, 1)
 # ------------------------------------------------------------
 from __future__ import annotations
 
@@ -18,14 +26,106 @@ from pathlib import Path
 from typing import Union
 
 import soundfile as sf
+from scipy.io import savemat
 
 from core.aac_configuration import WIN_TYPE
 from core.aac_filterbank import aac_filter_bank
-from core.aac_ssc import aac_SSC
+from core.aac_ssc import aac_ssc
 from core.aac_tns import aac_tns
+from core.aac_psycho import aac_psycho
+from core.aac_quantizer import aac_quantizer  # assumes your quantizer file is core/aac_quantizer.py
+from core.aac_huffman import aac_encode_huff
+from core.aac_utils import get_table, band_limits
+from material.huff_utils import load_LUT
+
 from core.aac_types import *
 
 
+
+# -----------------------------------------------------------------------------
+# Helpers for thresholds (T(b))
+# -----------------------------------------------------------------------------
+
+def _band_slices_from_table(frame_type: FrameType) -> list[tuple[int, int]]:
+    """
+    Return inclusive (lo, hi) band slices derived from TableB219.
+    """
+    table, _ = get_table(frame_type)
+    wlow, whigh, _bval, _qthr_db = band_limits(table)
+    return [(int(lo), int(hi)) for lo, hi in zip(wlow, whigh)]
+
+
+def _thresholds_from_smr(
+    frame_F_ch: FrameChannelF,
+    frame_type: FrameType,
+    SMR: FloatArray,
+) -> FloatArray:
+    """
+    Compute thresholds T(b) = P(b) / SMR(b), where P(b) is band energy.
+
+    Shapes:
+    - Long: returns (NB, 1)
+    - ESH: returns (NB, 8)
+    """
+    bands = _band_slices_from_table(frame_type)
+    NB = len(bands)
+
+    X = np.asarray(frame_F_ch, dtype=np.float64)
+    SMR = np.asarray(SMR, dtype=np.float64)
+
+    if frame_type == "ESH":
+        if X.shape != (128, 8):
+            raise ValueError("For ESH, frame_F_ch must have shape (128, 8).")
+        if SMR.shape != (NB, 8):
+            raise ValueError(f"For ESH, SMR must have shape ({NB}, 8).")
+
+        T = np.zeros((NB, 8), dtype=np.float64)
+        for j in range(8):
+            Xj = X[:, j]
+            for b, (lo, hi) in enumerate(bands):
+                P = float(np.sum(Xj[lo : hi + 1] ** 2))
+                smr = float(SMR[b, j])
+                T[b, j] = 0.0 if smr <= 1e-12 else (P / smr)
+        return T
+
+    # Long
+    if X.shape == (1024,):
+        Xv = X
+    elif X.shape == (1024, 1):
+        Xv = X[:, 0]
+    else:
+        raise ValueError("For non-ESH, frame_F_ch must be shape (1024,) or (1024, 1).")
+
+    if SMR.shape == (NB,):
+        SMRv = SMR
+    elif SMR.shape == (NB, 1):
+        SMRv = SMR[:, 0]
+    else:
+        raise ValueError(f"For non-ESH, SMR must be shape ({NB},) or ({NB}, 1).")
+
+    T = np.zeros((NB, 1), dtype=np.float64)
+    for b, (lo, hi) in enumerate(bands):
+        P = float(np.sum(Xv[lo : hi + 1] ** 2))
+        smr = float(SMRv[b])
+        T[b, 0] = 0.0 if smr <= 1e-12 else (P / smr)
+
+    return T
+
+def _normalize_global_gain(G: GlobalGain) -> float | FloatArray:
+    """
+    Normalize GlobalGain to match AACChannelFrameF3["G"] type:
+    - long: return float
+    - ESH: return float64 ndarray of shape (1, 8)
+    """
+    if np.isscalar(G):
+        return float(G)
+
+    G_arr = np.asarray(G)
+    if G_arr.size == 1:
+        return float(G_arr.reshape(-1)[0])
+
+    return np.asarray(G_arr, dtype=np.float64)
+
 # -----------------------------------------------------------------------------
 # Public helpers (useful for level_x demo wrappers)
 # -----------------------------------------------------------------------------
@@ -174,7 +274,7 @@ def aac_coder_1(filename_in: Union[str, Path]) -> AACSeq1:
             tail = np.zeros((win - next_t.shape[0], 2), dtype=np.float64)
             next_t = np.vstack([next_t, tail])
 
-        frame_type = aac_SSC(frame_t, next_t, prev_frame_type)
+        frame_type = aac_ssc(frame_t, next_t, prev_frame_type)
         frame_f = aac_filter_bank(frame_t, frame_type, win_type)
 
         chl_f, chr_f = aac_pack_frame_f_to_seq_channels(frame_type, frame_f)
@@ -191,10 +291,6 @@ def aac_coder_1(filename_in: Union[str, Path]) -> AACSeq1:
     return aac_seq
 
 
-# -----------------------------------------------------------------------------
-# Level 2 encoder
-# -----------------------------------------------------------------------------
-
 def aac_coder_2(filename_in: Union[str, Path]) -> AACSeq2:
     """
     Level-2 AAC encoder (Level 1 + TNS).
@@ -246,7 +342,7 @@ def aac_coder_2(filename_in: Union[str, Path]) -> AACSeq2:
             tail = np.zeros((win - next_t.shape[0], 2), dtype=np.float64)
             next_t = np.vstack([next_t, tail])
 
-        frame_type = aac_SSC(frame_t, next_t, prev_frame_type)
+        frame_type = aac_ssc(frame_t, next_t, prev_frame_type)
 
         # Level 1 analysis (packed stereo container)
         frame_f_stereo = aac_filter_bank(frame_t, frame_type, WIN_TYPE)
@@ -278,3 +374,180 @@ def aac_coder_2(filename_in: Union[str, Path]) -> AACSeq2:
         prev_frame_type = frame_type
 
     return aac_seq
+
+
+def aac_coder_3(
+    filename_in: Union[str, Path],
+    filename_aac_coded: Union[str, Path] | None = None,
+) -> AACSeq3:
+    """
+    Level-3 AAC encoder (Level 2 + Psycho + Quantizer + Huffman).
+
+    Parameters
+    ----------
+    filename_in : Union[str, Path]
+        Input WAV filename (stereo, 48 kHz).
+    filename_aac_coded : Union[str, Path] | None
+        Optional .mat filename to store aac_seq_3 (assignment convenience).
+
+    Returns
+    -------
+    AACSeq3
+        Encoded AAC sequence (Level 3 payload schema).
+    """
+    filename_in = Path(filename_in)
+
+    x, _ = aac_read_wav_stereo_48k(filename_in)
+
+    hop = 1024
+    win = 2048
+
+    pad_pre = np.zeros((hop, 2), dtype=np.float64)
+    pad_post = np.zeros((hop, 2), dtype=np.float64)
+    x_pad = np.vstack([pad_pre, x, pad_post])
+
+    K = int((x_pad.shape[0] - win) // hop + 1)
+    if K <= 0:
+        raise ValueError("Input too short for framing.")
+
+    # Load Huffman LUTs once.
+    huff_LUT_list = load_LUT()
+
+    aac_seq: AACSeq3 = []
+    prev_frame_type: FrameType = "OLS"
+
+    # Pin win_type to the WinType literal for type checkers.
+    win_type: WinType = WIN_TYPE
+
+    # Psycho model needs per-channel history (prev1, prev2) of 2048-sample frames.
+    prev1_L = np.zeros((2048,), dtype=np.float64)
+    prev2_L = np.zeros((2048,), dtype=np.float64)
+    prev1_R = np.zeros((2048,), dtype=np.float64)
+    prev2_R = np.zeros((2048,), dtype=np.float64)
+
+    for i in range(K):
+        start = i * hop
+
+        frame_t: FrameT = x_pad[start : start + win, :]
+        if frame_t.shape != (win, 2):
+            raise ValueError("Internal framing error: frame_t has wrong shape.")
+
+        next_t = x_pad[start + hop : start + hop + win, :]
+        if next_t.shape[0] < win:
+            tail = np.zeros((win - next_t.shape[0], 2), dtype=np.float64)
+            next_t = np.vstack([next_t, tail])
+
+        frame_type = aac_ssc(frame_t, next_t, prev_frame_type)
+
+        # Analysis filterbank (stereo packed)
+        frame_f_stereo = aac_filter_bank(frame_t, frame_type, win_type)
+        chl_f, chr_f = aac_pack_frame_f_to_seq_channels(frame_type, frame_f_stereo)
+
+        # TNS per channel
+        chl_f_tns, chl_tns_coeffs = aac_tns(chl_f, frame_type)
+        chr_f_tns, chr_tns_coeffs = aac_tns(chr_f, frame_type)
+
+        # Psychoacoustic model per channel (time-domain)
+        frame_L = np.asarray(frame_t[:, 0], dtype=np.float64)
+        frame_R = np.asarray(frame_t[:, 1], dtype=np.float64)
+
+        SMR_L = aac_psycho(frame_L, frame_type, prev1_L, prev2_L)
+        SMR_R = aac_psycho(frame_R, frame_type, prev1_R, prev2_R)
+
+        # Thresholds T(b) (stored, not entropy-coded)
+        T_L = _thresholds_from_smr(chl_f_tns, frame_type, SMR_L)
+        T_R = _thresholds_from_smr(chr_f_tns, frame_type, SMR_R)
+
+        # Quantizer per channel
+        S_L, sfc_L, G_L = aac_quantizer(chl_f_tns, frame_type, SMR_L)
+        S_R, sfc_R, G_R = aac_quantizer(chr_f_tns, frame_type, SMR_R)
+
+        # Normalize G types for AACSeq3 schema (float | float64 ndarray).
+        G_Ln = _normalize_global_gain(G_L)
+        G_Rn = _normalize_global_gain(G_R)
+
+        # Huffman-code ONLY the DPCM differences for b>0.
+        # sfc[0] corresponds to alpha(0)=G and is stored separately in the frame.
+        sfc_L_dpcm = np.asarray(sfc_L, dtype=np.int64)[1:, ...]
+        sfc_R_dpcm = np.asarray(sfc_R, dtype=np.int64)[1:, ...]
+
+        # Codebook 11:
+        # maxAbsCodeVal = 16 is RESERVED for ESCAPE.
+        # We must stay strictly within [-15, +15] to avoid escape decoding.
+        sf_cb = 11
+        sf_max_abs = int(huff_LUT_list[sf_cb]["maxAbsCodeVal"]) - 1  # -> 15
+
+        sfc_L_dpcm = np.clip(
+            sfc_L_dpcm,
+            -sf_max_abs,
+            sf_max_abs,
+        ).astype(np.int64, copy=False)
+
+        sfc_R_dpcm = np.clip(
+            sfc_R_dpcm,
+            -sf_max_abs,
+            sf_max_abs,
+        ).astype(np.int64, copy=False)
+
+        sfc_L_stream, _ = aac_encode_huff(
+            sfc_L_dpcm.reshape(-1, order="F"),
+            huff_LUT_list,
+            force_codebook=sf_cb,
+        )
+        sfc_R_stream, _ = aac_encode_huff(
+            sfc_R_dpcm.reshape(-1, order="F"),
+            huff_LUT_list,
+            force_codebook=sf_cb,
+        )
+
+        mdct_L_stream, cb_L = aac_encode_huff(
+            np.asarray(S_L, dtype=np.int64).reshape(-1),
+            huff_LUT_list,
+        )
+        mdct_R_stream, cb_R = aac_encode_huff(
+            np.asarray(S_R, dtype=np.int64).reshape(-1),
+            huff_LUT_list,
+        )
+
+        # Typed dict construction helps static analyzers validate the schema.
+        frame_out: AACSeq3Frame = {
+            "frame_type": frame_type,
+            "win_type": win_type,
+            "chl": {
+                "tns_coeffs": np.asarray(chl_tns_coeffs, dtype=np.float64),
+                "T": np.asarray(T_L, dtype=np.float64),
+                "G": G_Ln,
+                "sfc": sfc_L_stream,
+                "stream": mdct_L_stream,
+                "codebook": int(cb_L),
+            },
+            "chr": {
+                "tns_coeffs": np.asarray(chr_tns_coeffs, dtype=np.float64),
+                "T": np.asarray(T_R, dtype=np.float64),
+                "G": G_Rn,
+                "sfc": sfc_R_stream,
+                "stream": mdct_R_stream,
+                "codebook": int(cb_R),
+            },
+        }
+        aac_seq.append(frame_out)
+
+        # Update psycho history (shift register)
+        prev2_L = prev1_L
+        prev1_L = frame_L
+        prev2_R = prev1_R
+        prev1_R = frame_R
+
+        prev_frame_type = frame_type
+
+    # Optional: store to .mat for the assignment wrapper
+    if filename_aac_coded is not None:
+        filename_aac_coded = Path(filename_aac_coded)
+        savemat(
+            str(filename_aac_coded),
+            {"aac_seq_3": np.array(aac_seq, dtype=object)},
+            do_compression=True,
+        )
+
+    return aac_seq
+

source/level_1/core/aac_decoder.py

@@ -22,9 +22,22 @@ import soundfile as sf
 
 from core.aac_filterbank import aac_i_filter_bank
 from core.aac_tns import aac_i_tns
+from core.aac_quantizer import aac_i_quantizer
+from core.aac_huffman import aac_decode_huff
+from core.aac_utils import get_table, band_limits
+from material.huff_utils import load_LUT
 from core.aac_types import *
 
 
+# -----------------------------------------------------------------------------
+# Helper for NB
+# -----------------------------------------------------------------------------
+def _nbands(frame_type: FrameType) -> int:
+    table, _ = get_table(frame_type)
+    wlow, _whigh, _bval, _qthr_db = band_limits(table)
+    return int(len(wlow))
+
+
 # -----------------------------------------------------------------------------
 # Public helpers
 # -----------------------------------------------------------------------------
@@ -252,3 +265,144 @@ def aac_decoder_2(aac_seq_2: AACSeq2, filename_out: Union[str, Path]) -> StereoS
 
     sf.write(str(filename_out), y, 48000)
     return y
+
+
+
+def aac_decoder_3(aac_seq_3: AACSeq3, filename_out: Union[str, Path]) -> StereoSignal:
+    """
+    Level-3 AAC decoder (inverse of aac_coder_3).
+
+    Steps per frame:
+    - Huffman decode scalefactors (sfc) using codebook 11
+    - Huffman decode MDCT symbols (stream) using stored codebook
+    - iQuantizer -> MDCT coefficients after TNS
+    - iTNS using stored predictor coefficients
+    - IMDCT filterbank -> time domain
+    - Overlap-add, remove padding, write WAV
+
+    Parameters
+    ----------
+    aac_seq_3 : AACSeq3
+        Encoded sequence as produced by aac_coder_3.
+    filename_out : Union[str, Path]
+        Output WAV filename.
+
+    Returns
+    -------
+    StereoSignal
+        Decoded audio samples (time-domain), stereo, shape (N, 2), dtype float64.
+    """
+    filename_out = Path(filename_out)
+
+    hop = 1024
+    win = 2048
+    K = len(aac_seq_3)
+
+    if K <= 0:
+        raise ValueError("aac_seq_3 must contain at least one frame.")
+
+    # Load Huffman LUTs once.
+    huff_LUT_list = load_LUT()
+
+    n_pad = (K - 1) * hop + win
+    y_pad = np.zeros((n_pad, 2), dtype=np.float64)
+
+    for i, fr in enumerate(aac_seq_3):
+        frame_type: FrameType = fr["frame_type"]
+        win_type: WinType = fr["win_type"]
+
+        NB = _nbands(frame_type)
+        # We store G separately, so Huffman stream contains only (NB-1) DPCM differences.
+        sfc_len = (NB - 1) * (8 if frame_type == "ESH" else 1)
+
+        # -------------------------
+        # Left channel
+        # -------------------------
+        tns_L = np.asarray(fr["chl"]["tns_coeffs"], dtype=np.float64)
+        G_L = fr["chl"]["G"]
+        sfc_bits_L = fr["chl"]["sfc"]
+        mdct_bits_L = fr["chl"]["stream"]
+        cb_L = int(fr["chl"]["codebook"])
+
+        sfc_dec_L = aac_decode_huff(sfc_bits_L, 11, huff_LUT_list)[:sfc_len].astype(np.int64, copy=False)
+        if frame_type == "ESH":
+            sfc_dpcm_L = sfc_dec_L.reshape(NB - 1, 8, order="F")
+            sfc_L = np.zeros((NB, 8), dtype=np.int64)
+            Gv = np.asarray(G_L, dtype=np.float64).reshape(1, 8)
+            sfc_L[0, :] = Gv[0, :].astype(np.int64)
+            sfc_L[1:, :] = sfc_dpcm_L
+        else:
+            sfc_dpcm_L = sfc_dec_L.reshape(NB - 1, 1, order="F")
+            sfc_L = np.zeros((NB, 1), dtype=np.int64)
+            sfc_L[0, 0] = int(float(G_L))
+            sfc_L[1:, :] = sfc_dpcm_L
+
+        # MDCT symbols: codebook 0 means "all-zero section"
+        if cb_L == 0:
+            S_dec_L = np.zeros((1024,), dtype=np.int64)
+        else:
+            S_tmp_L = aac_decode_huff(mdct_bits_L, cb_L, huff_LUT_list).astype(np.int64, copy=False)
+
+            # Tuple coding may produce extra trailing symbols; caller knows the true length (1024).
+            # Also guard against short outputs by zero-padding.
+            if S_tmp_L.size < 1024:
+                S_dec_L = np.zeros((1024,), dtype=np.int64)
+                S_dec_L[: S_tmp_L.size] = S_tmp_L
+            else:
+                S_dec_L = S_tmp_L[:1024]
+
+        S_L = S_dec_L.reshape(1024, 1)
+
+        Xq_L = aac_i_quantizer(S_L, sfc_L, G_L, frame_type)
+        X_L = aac_i_tns(Xq_L, frame_type, tns_L)
+
+        # -------------------------
+        # Right channel
+        # -------------------------
+        tns_R = np.asarray(fr["chr"]["tns_coeffs"], dtype=np.float64)
+        G_R = fr["chr"]["G"]
+        sfc_bits_R = fr["chr"]["sfc"]
+        mdct_bits_R = fr["chr"]["stream"]
+        cb_R = int(fr["chr"]["codebook"])
+
+        sfc_dec_R = aac_decode_huff(sfc_bits_R, 11, huff_LUT_list)[:sfc_len].astype(np.int64, copy=False)
+        if frame_type == "ESH":
+            sfc_dpcm_R = sfc_dec_R.reshape(NB - 1, 8, order="F")
+            sfc_R = np.zeros((NB, 8), dtype=np.int64)
+            Gv = np.asarray(G_R, dtype=np.float64).reshape(1, 8)
+            sfc_R[0, :] = Gv[0, :].astype(np.int64)
+            sfc_R[1:, :] = sfc_dpcm_R
+        else:
+            sfc_dpcm_R = sfc_dec_R.reshape(NB - 1, 1, order="F")
+            sfc_R = np.zeros((NB, 1), dtype=np.int64)
+            sfc_R[0, 0] = int(float(G_R))
+            sfc_R[1:, :] = sfc_dpcm_R
+
+        if cb_R == 0:
+            S_dec_R = np.zeros((1024,), dtype=np.int64)
+        else:
+            S_tmp_R = aac_decode_huff(mdct_bits_R, cb_R, huff_LUT_list).astype(np.int64, copy=False)
+
+            if S_tmp_R.size < 1024:
+                S_dec_R = np.zeros((1024,), dtype=np.int64)
+                S_dec_R[: S_tmp_R.size] = S_tmp_R
+            else:
+                S_dec_R = S_tmp_R[:1024]
+
+        S_R = S_dec_R.reshape(1024, 1)
+
+        Xq_R = aac_i_quantizer(S_R, sfc_R, G_R, frame_type)
+        X_R = aac_i_tns(Xq_R, frame_type, tns_R)
+
+        # Re-pack to stereo container and inverse filterbank
+        frame_f = aac_unpack_seq_channels_to_frame_f(frame_type, np.asarray(X_L), np.asarray(X_R))
+        frame_t_hat: FrameT = aac_i_filter_bank(frame_f, frame_type, win_type)
+
+        start = i * hop
+        y_pad[start : start + win, :] += frame_t_hat
+
+    y = aac_remove_padding(y_pad, hop=hop)
+
+    sf.write(str(filename_out), y, 48000)
+    return y
+

source/level_1/core/aac_ssc.py

@@ -176,7 +176,7 @@ def _stereo_merge(ft_l: FrameType, ft_r: FrameType) -> FrameType:
 # Public Function prototypes
 # -----------------------------------------------------------------------------
 
-def aac_SSC(frame_T: FrameT, next_frame_T: FrameT, prev_frame_type: FrameType) -> FrameType:
+def aac_ssc(frame_T: FrameT, next_frame_T: FrameT, prev_frame_type: FrameType) -> FrameType:
     """
     Sequence Segmentation Control (SSC).
 

source/level_1/core/aac_types.py

@@ -212,6 +212,42 @@ BandValueArray: TypeAlias = FloatArray
 Per-band psychoacoustic values (e.g. Bark position, thresholds).
 """
 
+
+# Quantizer-related semantic aliases
+
+QuantizedSymbols: TypeAlias = NDArray[np.generic]
+"""
+Quantized MDCT symbols S(k).
+
+Shapes:
+- Always (1024, 1) at the quantizer output (ESH packed to 1024 symbols).
+"""
+
+ScaleFactors: TypeAlias = NDArray[np.generic]
+"""
+DPCM-coded scalefactors sfc(b) = alpha(b) - alpha(b-1).
+
+Shapes:
+- Long frames: (NB, 1)
+- ESH frames: (NB, 8)
+"""
+
+GlobalGain: TypeAlias = float | NDArray[np.generic]
+"""
+Global gain G = alpha(0).
+
+- Long frames: scalar float
+- ESH frames: array shape (1, 8)
+"""
+
+# Huffman semantic aliases
+
+HuffmanBitstream: TypeAlias = str
+"""Huffman-coded bitstream stored as a string of '0'/'1'."""
+
+HuffmanCodebook: TypeAlias = int
+"""Huffman codebook id (e.g., 0..11)."""
+
 # -----------------------------------------------------------------------------
 # Level 1 AAC sequence payload types
 # -----------------------------------------------------------------------------
@@ -299,3 +335,77 @@ Level 2 adds:
 and stores:
 - per-channel "frame_F" after applying TNS.
 """
+
+# -----------------------------------------------------------------------------
+# Level 3 AAC sequence payload types (Quantizer + Huffman)
+# -----------------------------------------------------------------------------
+
+class AACChannelFrameF3(TypedDict):
+    """
+    Per-channel payload for aac_seq_3[i]["chl"] or ["chr"] (Level 3).
+
+    Keys
+    ----
+    tns_coeffs:
+        Quantized TNS predictor coefficients for ONE channel.
+        Shapes:
+        - ESH: (PRED_ORDER, 8)
+        - else: (PRED_ORDER, 1)
+
+    T:
+        Psychoacoustic thresholds per band.
+        Shapes:
+        - ESH: (NB, 8)
+        - else: (NB, 1)
+        Note: Stored for completeness / debugging; not entropy-coded.
+
+    G:
+        Quantized global gains.
+        Shapes:
+        - ESH: (1, 8)  (one per short subframe)
+        - else: scalar (or compatible np scalar)
+
+    sfc:
+        Huffman-coded scalefactor differences (DPCM sequence).
+
+    stream:
+        Huffman-coded MDCT quantized symbols S(k) (packed to 1024 symbols).
+
+    codebook:
+        Huffman codebook id used for MDCT symbols (stream).
+        (Scalefactors typically use fixed codebook 11 and do not need to store it.)
+    """
+    tns_coeffs: TnsCoeffs
+    T: FloatArray
+    G: FloatArray | float
+    sfc: HuffmanBitstream
+    stream: HuffmanBitstream
+    codebook: HuffmanCodebook
+
+
+class AACSeq3Frame(TypedDict):
+    """
+    One frame dictionary element of aac_seq_3 (Level 3).
+    """
+    frame_type: FrameType
+    win_type: WinType
+    chl: AACChannelFrameF3
+    chr: AACChannelFrameF3
+
+
+AACSeq3: TypeAlias = List[AACSeq3Frame]
+"""
+AAC sequence for Level 3:
+List of length K (K = number of frames).
+
+Each element is a dict with keys:
+- "frame_type", "win_type", "chl", "chr"
+
+Level 3 adds (per channel):
+- "tns_coeffs"
+- "T" thresholds (not entropy-coded)
+- "G" global gain(s)
+- "sfc" Huffman-coded scalefactor differences
+- "stream" Huffman-coded MDCT quantized symbols
+- "codebook" Huffman codebook for MDCT symbols
+"""

source/level_1/material/huff_utils.py

@@ -1,400 +0,0 @@
-import numpy as np
-import scipy.io as sio
-import os
-
-# ------------------ LOAD LUT ------------------
-
-def load_LUT(mat_filename=None):
-    """
-    Loads the list of Huffman Codebooks (LUTs)
-
-    Returns:
-        huffLUT : list (index 1..11 used, index 0 unused)
-    """
-    if mat_filename is None:
-        current_dir = os.path.dirname(os.path.abspath(__file__))
-        mat_filename = os.path.join(current_dir, "huffCodebooks.mat")
-
-    mat = sio.loadmat(mat_filename)
-
-
-    huffCodebooks_raw = mat['huffCodebooks'].squeeze()
-
-    huffCodebooks = []
-    for i in range(11):
-        huffCodebooks.append(np.array(huffCodebooks_raw[i]))
-
-    # Build inverse VLC tables
-    invTable = [None] * 11
-
-    for i in range(11):
-        h = huffCodebooks[i][:, 2].astype(int)       # column 3
-        hlength = huffCodebooks[i][:, 1].astype(int) # column 2
-
-        hbin = []
-        for j in range(len(h)):
-            hbin.append(format(h[j], f'0{hlength[j]}b'))
-
-        invTable[i] = vlc_table(hbin)
-
-    # Build Huffman LUT dicts
-    huffLUT = [None] * 12  # index 0 unused
-    params = [
-        (4, 1, True),
-        (4, 1, True),
-        (4, 2, False),
-        (4, 2, False),
-        (2, 4, True),
-        (2, 4, True),
-        (2, 7, False),
-        (2, 7, False),
-        (2, 12, False),
-        (2, 12, False),
-        (2, 16, False),
-    ]
-
-    for i, (nTupleSize, maxAbs, signed) in enumerate(params, start=1):
-        huffLUT[i] = {
-            'LUT': huffCodebooks[i-1],
-            'invTable': invTable[i-1],
-            'codebook': i,
-            'nTupleSize': nTupleSize,
-            'maxAbsCodeVal': maxAbs,
-            'signedValues': signed
-        }
-
-    return huffLUT
-
-def vlc_table(code_array):
-    """
-    codeArray: list of strings, each string is a Huffman codeword (e.g. '0101')
-    returns:
-        h : NumPy array of shape (num_nodes, 3)
-            columns:
-              [ next_if_0 , next_if_1 , symbol_index ]
-    """
-    h = np.zeros((1, 3), dtype=int)
-
-    for code_index, code in enumerate(code_array, start=1):
-        word = [int(bit) for bit in code]
-        h_index = 0
-
-        for bit in word:
-            k = bit
-            next_node = h[h_index, k]
-            if next_node == 0:
-                h = np.vstack([h, [0, 0, 0]])
-                new_index = h.shape[0] - 1
-                h[h_index, k] = new_index
-                h_index = new_index
-            else:
-                h_index = next_node
-
-        h[h_index, 2] = code_index
-
-    return h
-
-# ------------------ ENCODE ------------------
-
-def encode_huff(coeff_sec, huff_LUT_list, force_codebook = None):
-    """
-    Huffman-encode a sequence of quantized coefficients.
-
-    This function selects the appropriate Huffman codebook based on the
-    maximum absolute value of the input coefficients, encodes the coefficients
-    into a binary Huffman bitstream, and returns both the bitstream and the
-    selected codebook index.
-
-    This is the Python equivalent of the MATLAB `encodeHuff.m` function used
-    in audio/image coding (e.g., scale factor band encoding). The input
-    coefficient sequence is grouped into fixed-size tuples as defined by
-    the chosen Huffman LUT. Zero-padding may be applied internally.
-
-    Parameters
-    ----------
-    coeff_sec : array_like of int
-        1-D array of quantized integer coefficients to encode.
-        Typically corresponds to a "section" or scale-factor band.
-
-    huff_LUT_list : list
-        List of Huffman lookup-table dictionaries as returned by `loadLUT()`.
-        Index 1..11 correspond to valid Huffman codebooks.
-        Index 0 is unused.
-
-    Returns
-    -------
-    huffSec : str
-        Huffman-encoded bitstream represented as a string of '0' and '1'
-        characters.
-
-    huffCodebook : int
-        Index (1..11) of the Huffman codebook used for encoding.
-        A value of 0 indicates a special all-zero section.
-    """
-    if force_codebook is not None:
-            return huff_LUT_code_1(huff_LUT_list[force_codebook], coeff_sec)
-    
-    maxAbsVal = np.max(np.abs(coeff_sec))
-
-    if maxAbsVal == 0:
-        huffCodebook = 0
-        huffSec = huff_LUT_code_0()
-
-    elif maxAbsVal == 1:
-        candidates = [1, 2]
-        huffSec1 = huff_LUT_code_1(huff_LUT_list[candidates[0]], coeff_sec)
-        huffSec2 = huff_LUT_code_1(huff_LUT_list[candidates[1]], coeff_sec)
-        if len(huffSec1) <= len(huffSec2):
-            huffSec = huffSec1
-            huffCodebook = candidates[0]
-        else:
-            huffSec = huffSec2
-            huffCodebook = candidates[1]
-
-    elif maxAbsVal == 2:
-        candidates = [3, 4]
-        huffSec1 = huff_LUT_code_1(huff_LUT_list[candidates[0]], coeff_sec)
-        huffSec2 = huff_LUT_code_1(huff_LUT_list[candidates[1]], coeff_sec)
-        if len(huffSec1) <= len(huffSec2):
-            huffSec = huffSec1
-            huffCodebook = candidates[0]
-        else:
-            huffSec = huffSec2
-            huffCodebook = candidates[1]
-
-    elif maxAbsVal in (3, 4):
-        candidates = [5, 6]
-        huffSec1 = huff_LUT_code_1(huff_LUT_list[candidates[0]], coeff_sec)
-        huffSec2 = huff_LUT_code_1(huff_LUT_list[candidates[1]], coeff_sec)
-        if len(huffSec1) <= len(huffSec2):
-            huffSec = huffSec1
-            huffCodebook = candidates[0]
-        else:
-            huffSec = huffSec2
-            huffCodebook = candidates[1]
-
-    elif maxAbsVal in (5, 6, 7):
-        candidates = [7, 8]
-        huffSec1 = huff_LUT_code_1(huff_LUT_list[candidates[0]], coeff_sec)
-        huffSec2 = huff_LUT_code_1(huff_LUT_list[candidates[1]], coeff_sec)
-        if len(huffSec1) <= len(huffSec2):
-            huffSec = huffSec1
-            huffCodebook = candidates[0]
-        else:
-            huffSec = huffSec2
-            huffCodebook = candidates[1]
-
-    elif maxAbsVal in (8, 9, 10, 11, 12):
-        candidates = [9, 10]
-        huffSec1 = huff_LUT_code_1(huff_LUT_list[candidates[0]], coeff_sec)
-        huffSec2 = huff_LUT_code_1(huff_LUT_list[candidates[1]], coeff_sec)
-        if len(huffSec1) <= len(huffSec2):
-            huffSec = huffSec1
-            huffCodebook = candidates[0]
-        else:
-            huffSec = huffSec2
-            huffCodebook = candidates[1]
-
-    elif maxAbsVal in (13, 14, 15):
-        huffCodebook = 11
-        huffSec = huff_LUT_code_1(huff_LUT_list[huffCodebook], coeff_sec)
-
-    else:
-        huffCodebook = 11
-        huffSec = huff_LUT_code_ESC(huff_LUT_list[huffCodebook], coeff_sec)
-
-    return huffSec, huffCodebook
-
-def huff_LUT_code_1(huff_LUT, coeff_sec):
-    LUT = huff_LUT['LUT']
-    nTupleSize = huff_LUT['nTupleSize']
-    maxAbsCodeVal = huff_LUT['maxAbsCodeVal']
-    signedValues = huff_LUT['signedValues']
-
-    numTuples = int(np.ceil(len(coeff_sec) / nTupleSize))
-
-    if signedValues:
-        coeff = coeff_sec + maxAbsCodeVal
-        base = 2 * maxAbsCodeVal + 1
-    else:
-        coeff = coeff_sec
-        base = maxAbsCodeVal + 1
-
-    coeffPad = np.zeros(numTuples * nTupleSize, dtype=int)
-    coeffPad[:len(coeff)] = coeff
-
-    huffSec = []
-
-    powers = base ** np.arange(nTupleSize - 1, -1, -1)
-
-    for i in range(numTuples):
-        nTuple = coeffPad[i*nTupleSize:(i+1)*nTupleSize]
-        huffIndex = int(np.abs(nTuple) @ powers)
-
-        hexVal = LUT[huffIndex, 2]
-        huffLen = LUT[huffIndex, 1]
-
-        bits = format(int(hexVal), f'0{int(huffLen)}b')
-
-        if signedValues:
-            huffSec.append(bits)
-        else:
-            signBits = ''.join('1' if v < 0 else '0' for v in nTuple)
-            huffSec.append(bits + signBits)
-
-    return ''.join(huffSec)
-
-def huff_LUT_code_0():
-    return ''
-
-def huff_LUT_code_ESC(huff_LUT, coeff_sec):
-    LUT = huff_LUT['LUT']
-    nTupleSize = huff_LUT['nTupleSize']
-    maxAbsCodeVal = huff_LUT['maxAbsCodeVal']
-
-    numTuples = int(np.ceil(len(coeff_sec) / nTupleSize))
-    base = maxAbsCodeVal + 1
-
-    coeffPad = np.zeros(numTuples * nTupleSize, dtype=int)
-    coeffPad[:len(coeff_sec)] = coeff_sec
-
-    huffSec = []
-    powers = base ** np.arange(nTupleSize - 1, -1, -1)
-
-    for i in range(numTuples):
-        nTuple = coeffPad[i*nTupleSize:(i+1)*nTupleSize]
-
-        lnTuple = nTuple.astype(float)
-        lnTuple[lnTuple == 0] = np.finfo(float).eps
-
-        N4 = np.maximum(0, np.floor(np.log2(np.abs(lnTuple))).astype(int))
-        N = np.maximum(0, N4 - 4)
-        esc = np.abs(nTuple) > 15
-
-        nTupleESC = nTuple.copy()
-        nTupleESC[esc] = np.sign(nTupleESC[esc]) * 16
-
-        huffIndex = int(np.abs(nTupleESC) @ powers)
-
-        hexVal = LUT[huffIndex, 2]
-        huffLen = LUT[huffIndex, 1]
-
-        bits = format(int(hexVal), f'0{int(huffLen)}b')
-
-        escSeq = ''
-        for k in range(nTupleSize):
-            if esc[k]:
-                escSeq += '1' * N[k]
-                escSeq += '0'
-                escSeq += format(abs(nTuple[k]) - (1 << N4[k]), f'0{N4[k]}b')
-
-        signBits = ''.join('1' if v < 0 else '0' for v in nTuple)
-        huffSec.append(bits + signBits + escSeq)
-
-    return ''.join(huffSec)
-
-# ------------------ DECODE ------------------
-
-def decode_huff(huff_sec, huff_LUT):
-    """
-    Decode a Huffman-encoded stream.
-
-    Parameters
-    ----------
-    huff_sec : array-like of int or str
-        Huffman encoded stream as a sequence of 0 and 1 (string or list/array).
-    huff_LUT : dict
-        Huffman lookup table with keys:
-            - 'invTable': inverse table (numpy array)
-            - 'codebook': codebook number
-            - 'nTupleSize': tuple size
-            - 'maxAbsCodeVal': maximum absolute code value
-            - 'signedValues': True/False
-
-    Returns
-    -------
-    decCoeffs : list of int
-        Decoded quantized coefficients.
-    """
-
-    h = huff_LUT['invTable']
-    huffCodebook = huff_LUT['codebook']
-    nTupleSize = huff_LUT['nTupleSize']
-    maxAbsCodeVal = huff_LUT['maxAbsCodeVal']
-    signedValues = huff_LUT['signedValues']
-
-    # Convert string to array of ints
-    if isinstance(huff_sec, str):
-        huff_sec = np.array([int(b) for b in huff_sec])
-
-    eos = False
-    decCoeffs = []
-    streamIndex = 0
-
-    while not eos:
-        wordbit = 0
-        r = 0  # start at root
-
-        # Decode Huffman word using inverse table
-        while True:
-            b = huff_sec[streamIndex + wordbit]
-            wordbit += 1
-            rOld = r
-            r = h[rOld, b]
-            if h[r, 0] == 0 and h[r, 1] == 0:
-                symbolIndex = h[r, 2] - 1  # zero-based
-                streamIndex += wordbit
-                break
-
-        # Decode n-tuple magnitudes
-        if signedValues:
-            base = 2 * maxAbsCodeVal + 1
-            nTupleDec = []
-            tmp = symbolIndex
-            for p in reversed(range(nTupleSize)):
-                val = tmp // (base ** p)
-                nTupleDec.append(val - maxAbsCodeVal)
-                tmp = tmp % (base ** p)
-            nTupleDec = np.array(nTupleDec)
-        else:
-            base = maxAbsCodeVal + 1
-            nTupleDec = []
-            tmp = symbolIndex
-            for p in reversed(range(nTupleSize)):
-                val = tmp // (base ** p)
-                nTupleDec.append(val)
-                tmp = tmp % (base ** p)
-            nTupleDec = np.array(nTupleDec)
-
-            # Apply sign bits
-            nTupleSignBits = huff_sec[streamIndex:streamIndex + nTupleSize]
-            nTupleSign = -(np.sign(nTupleSignBits - 0.5))
-            streamIndex += nTupleSize
-            nTupleDec = nTupleDec * nTupleSign
-
-        # Handle escape sequences
-        escIndex = np.where(np.abs(nTupleDec) == 16)[0]
-        if huffCodebook == 11 and escIndex.size > 0:
-            for idx in escIndex:
-                N = 0
-                b = huff_sec[streamIndex]
-                while b:
-                    N += 1
-                    b = huff_sec[streamIndex + N]
-                streamIndex += N
-                N4 = N + 4
-                escape_word = huff_sec[streamIndex:streamIndex + N4]
-                escape_value = 2 ** N4 + int("".join(map(str, escape_word)), 2)
-                nTupleDec[idx] = escape_value
-                streamIndex += N4 + 1
-            # Apply signs again
-            nTupleDec[escIndex] *= nTupleSign[escIndex]
-
-        decCoeffs.extend(nTupleDec.tolist())
-
-        if streamIndex >= len(huff_sec):
-            eos = True
-
-    return decCoeffs
-    
-

source/level_2/core/aac_coder.py

@@ -9,8 +9,16 @@
 #   cchoutou@ece.auth.gr
 #
 # Description:
-#   - Level 1 AAC encoder orchestration.
+#   Level 1 AAC encoder orchestration.
-#   - Level 2 AAC encoder orchestration.
+#   Keeps the same functional behavior as the original level_1 implementation:
+#   - Reads WAV via soundfile
+#   - Validates stereo and 48 kHz
+#   - Frames into 2048 samples with hop=1024 and zero padding at both ends
+#   - SSC decision uses next-frame attack detection
+#   - Filterbank analysis (MDCT)
+#   - Stores per-channel spectra in AACSeq1 schema:
+#       * ESH: (128, 8)
+#       * else: (1024, 1)
 # ------------------------------------------------------------
 from __future__ import annotations
 
@@ -18,14 +26,106 @@ from pathlib import Path
 from typing import Union
 
 import soundfile as sf
+from scipy.io import savemat
 
 from core.aac_configuration import WIN_TYPE
 from core.aac_filterbank import aac_filter_bank
-from core.aac_ssc import aac_SSC
+from core.aac_ssc import aac_ssc
 from core.aac_tns import aac_tns
+from core.aac_psycho import aac_psycho
+from core.aac_quantizer import aac_quantizer  # assumes your quantizer file is core/aac_quantizer.py
+from core.aac_huffman import aac_encode_huff
+from core.aac_utils import get_table, band_limits
+from material.huff_utils import load_LUT
+
 from core.aac_types import *
 
 
+
+# -----------------------------------------------------------------------------
+# Helpers for thresholds (T(b))
+# -----------------------------------------------------------------------------
+
+def _band_slices_from_table(frame_type: FrameType) -> list[tuple[int, int]]:
+    """
+    Return inclusive (lo, hi) band slices derived from TableB219.
+    """
+    table, _ = get_table(frame_type)
+    wlow, whigh, _bval, _qthr_db = band_limits(table)
+    return [(int(lo), int(hi)) for lo, hi in zip(wlow, whigh)]
+
+
+def _thresholds_from_smr(
+    frame_F_ch: FrameChannelF,
+    frame_type: FrameType,
+    SMR: FloatArray,
+) -> FloatArray:
+    """
+    Compute thresholds T(b) = P(b) / SMR(b), where P(b) is band energy.
+
+    Shapes:
+    - Long: returns (NB, 1)
+    - ESH: returns (NB, 8)
+    """
+    bands = _band_slices_from_table(frame_type)
+    NB = len(bands)
+
+    X = np.asarray(frame_F_ch, dtype=np.float64)
+    SMR = np.asarray(SMR, dtype=np.float64)
+
+    if frame_type == "ESH":
+        if X.shape != (128, 8):
+            raise ValueError("For ESH, frame_F_ch must have shape (128, 8).")
+        if SMR.shape != (NB, 8):
+            raise ValueError(f"For ESH, SMR must have shape ({NB}, 8).")
+
+        T = np.zeros((NB, 8), dtype=np.float64)
+        for j in range(8):
+            Xj = X[:, j]
+            for b, (lo, hi) in enumerate(bands):
+                P = float(np.sum(Xj[lo : hi + 1] ** 2))
+                smr = float(SMR[b, j])
+                T[b, j] = 0.0 if smr <= 1e-12 else (P / smr)
+        return T
+
+    # Long
+    if X.shape == (1024,):
+        Xv = X
+    elif X.shape == (1024, 1):
+        Xv = X[:, 0]
+    else:
+        raise ValueError("For non-ESH, frame_F_ch must be shape (1024,) or (1024, 1).")
+
+    if SMR.shape == (NB,):
+        SMRv = SMR
+    elif SMR.shape == (NB, 1):
+        SMRv = SMR[:, 0]
+    else:
+        raise ValueError(f"For non-ESH, SMR must be shape ({NB},) or ({NB}, 1).")
+
+    T = np.zeros((NB, 1), dtype=np.float64)
+    for b, (lo, hi) in enumerate(bands):
+        P = float(np.sum(Xv[lo : hi + 1] ** 2))
+        smr = float(SMRv[b])
+        T[b, 0] = 0.0 if smr <= 1e-12 else (P / smr)
+
+    return T
+
+def _normalize_global_gain(G: GlobalGain) -> float | FloatArray:
+    """
+    Normalize GlobalGain to match AACChannelFrameF3["G"] type:
+    - long: return float
+    - ESH: return float64 ndarray of shape (1, 8)
+    """
+    if np.isscalar(G):
+        return float(G)
+
+    G_arr = np.asarray(G)
+    if G_arr.size == 1:
+        return float(G_arr.reshape(-1)[0])
+
+    return np.asarray(G_arr, dtype=np.float64)
+
 # -----------------------------------------------------------------------------
 # Public helpers (useful for level_x demo wrappers)
 # -----------------------------------------------------------------------------
@@ -174,7 +274,7 @@ def aac_coder_1(filename_in: Union[str, Path]) -> AACSeq1:
             tail = np.zeros((win - next_t.shape[0], 2), dtype=np.float64)
             next_t = np.vstack([next_t, tail])
 
-        frame_type = aac_SSC(frame_t, next_t, prev_frame_type)
+        frame_type = aac_ssc(frame_t, next_t, prev_frame_type)
         frame_f = aac_filter_bank(frame_t, frame_type, win_type)
 
         chl_f, chr_f = aac_pack_frame_f_to_seq_channels(frame_type, frame_f)
@@ -191,10 +291,6 @@ def aac_coder_1(filename_in: Union[str, Path]) -> AACSeq1:
     return aac_seq
 
 
-# -----------------------------------------------------------------------------
-# Level 2 encoder
-# -----------------------------------------------------------------------------
-
 def aac_coder_2(filename_in: Union[str, Path]) -> AACSeq2:
     """
     Level-2 AAC encoder (Level 1 + TNS).
@@ -246,7 +342,7 @@ def aac_coder_2(filename_in: Union[str, Path]) -> AACSeq2:
             tail = np.zeros((win - next_t.shape[0], 2), dtype=np.float64)
             next_t = np.vstack([next_t, tail])
 
-        frame_type = aac_SSC(frame_t, next_t, prev_frame_type)
+        frame_type = aac_ssc(frame_t, next_t, prev_frame_type)
 
         # Level 1 analysis (packed stereo container)
         frame_f_stereo = aac_filter_bank(frame_t, frame_type, WIN_TYPE)
@@ -278,3 +374,180 @@ def aac_coder_2(filename_in: Union[str, Path]) -> AACSeq2:
         prev_frame_type = frame_type
 
     return aac_seq
+
+
+def aac_coder_3(
+    filename_in: Union[str, Path],
+    filename_aac_coded: Union[str, Path] | None = None,
+) -> AACSeq3:
+    """
+    Level-3 AAC encoder (Level 2 + Psycho + Quantizer + Huffman).
+
+    Parameters
+    ----------
+    filename_in : Union[str, Path]
+        Input WAV filename (stereo, 48 kHz).
+    filename_aac_coded : Union[str, Path] | None
+        Optional .mat filename to store aac_seq_3 (assignment convenience).
+
+    Returns
+    -------
+    AACSeq3
+        Encoded AAC sequence (Level 3 payload schema).
+    """
+    filename_in = Path(filename_in)
+
+    x, _ = aac_read_wav_stereo_48k(filename_in)
+
+    hop = 1024
+    win = 2048
+
+    pad_pre = np.zeros((hop, 2), dtype=np.float64)
+    pad_post = np.zeros((hop, 2), dtype=np.float64)
+    x_pad = np.vstack([pad_pre, x, pad_post])
+
+    K = int((x_pad.shape[0] - win) // hop + 1)
+    if K <= 0:
+        raise ValueError("Input too short for framing.")
+
+    # Load Huffman LUTs once.
+    huff_LUT_list = load_LUT()
+
+    aac_seq: AACSeq3 = []
+    prev_frame_type: FrameType = "OLS"
+
+    # Pin win_type to the WinType literal for type checkers.
+    win_type: WinType = WIN_TYPE
+
+    # Psycho model needs per-channel history (prev1, prev2) of 2048-sample frames.
+    prev1_L = np.zeros((2048,), dtype=np.float64)
+    prev2_L = np.zeros((2048,), dtype=np.float64)
+    prev1_R = np.zeros((2048,), dtype=np.float64)
+    prev2_R = np.zeros((2048,), dtype=np.float64)
+
+    for i in range(K):
+        start = i * hop
+
+        frame_t: FrameT = x_pad[start : start + win, :]
+        if frame_t.shape != (win, 2):
+            raise ValueError("Internal framing error: frame_t has wrong shape.")
+
+        next_t = x_pad[start + hop : start + hop + win, :]
+        if next_t.shape[0] < win:
+            tail = np.zeros((win - next_t.shape[0], 2), dtype=np.float64)
+            next_t = np.vstack([next_t, tail])
+
+        frame_type = aac_ssc(frame_t, next_t, prev_frame_type)
+
+        # Analysis filterbank (stereo packed)
+        frame_f_stereo = aac_filter_bank(frame_t, frame_type, win_type)
+        chl_f, chr_f = aac_pack_frame_f_to_seq_channels(frame_type, frame_f_stereo)
+
+        # TNS per channel
+        chl_f_tns, chl_tns_coeffs = aac_tns(chl_f, frame_type)
+        chr_f_tns, chr_tns_coeffs = aac_tns(chr_f, frame_type)
+
+        # Psychoacoustic model per channel (time-domain)
+        frame_L = np.asarray(frame_t[:, 0], dtype=np.float64)
+        frame_R = np.asarray(frame_t[:, 1], dtype=np.float64)
+
+        SMR_L = aac_psycho(frame_L, frame_type, prev1_L, prev2_L)
+        SMR_R = aac_psycho(frame_R, frame_type, prev1_R, prev2_R)
+
+        # Thresholds T(b) (stored, not entropy-coded)
+        T_L = _thresholds_from_smr(chl_f_tns, frame_type, SMR_L)
+        T_R = _thresholds_from_smr(chr_f_tns, frame_type, SMR_R)
+
+        # Quantizer per channel
+        S_L, sfc_L, G_L = aac_quantizer(chl_f_tns, frame_type, SMR_L)
+        S_R, sfc_R, G_R = aac_quantizer(chr_f_tns, frame_type, SMR_R)
+
+        # Normalize G types for AACSeq3 schema (float | float64 ndarray).
+        G_Ln = _normalize_global_gain(G_L)
+        G_Rn = _normalize_global_gain(G_R)
+
+        # Huffman-code ONLY the DPCM differences for b>0.
+        # sfc[0] corresponds to alpha(0)=G and is stored separately in the frame.
+        sfc_L_dpcm = np.asarray(sfc_L, dtype=np.int64)[1:, ...]
+        sfc_R_dpcm = np.asarray(sfc_R, dtype=np.int64)[1:, ...]
+
+        # Codebook 11:
+        # maxAbsCodeVal = 16 is RESERVED for ESCAPE.
+        # We must stay strictly within [-15, +15] to avoid escape decoding.
+        sf_cb = 11
+        sf_max_abs = int(huff_LUT_list[sf_cb]["maxAbsCodeVal"]) - 1  # -> 15
+
+        sfc_L_dpcm = np.clip(
+            sfc_L_dpcm,
+            -sf_max_abs,
+            sf_max_abs,
+        ).astype(np.int64, copy=False)
+
+        sfc_R_dpcm = np.clip(
+            sfc_R_dpcm,
+            -sf_max_abs,
+            sf_max_abs,
+        ).astype(np.int64, copy=False)
+
+        sfc_L_stream, _ = aac_encode_huff(
+            sfc_L_dpcm.reshape(-1, order="F"),
+            huff_LUT_list,
+            force_codebook=sf_cb,
+        )
+        sfc_R_stream, _ = aac_encode_huff(
+            sfc_R_dpcm.reshape(-1, order="F"),
+            huff_LUT_list,
+            force_codebook=sf_cb,
+        )
+
+        mdct_L_stream, cb_L = aac_encode_huff(
+            np.asarray(S_L, dtype=np.int64).reshape(-1),
+            huff_LUT_list,
+        )
+        mdct_R_stream, cb_R = aac_encode_huff(
+            np.asarray(S_R, dtype=np.int64).reshape(-1),
+            huff_LUT_list,
+        )
+
+        # Typed dict construction helps static analyzers validate the schema.
+        frame_out: AACSeq3Frame = {
+            "frame_type": frame_type,
+            "win_type": win_type,
+            "chl": {
+                "tns_coeffs": np.asarray(chl_tns_coeffs, dtype=np.float64),
+                "T": np.asarray(T_L, dtype=np.float64),
+                "G": G_Ln,
+                "sfc": sfc_L_stream,
+                "stream": mdct_L_stream,
+                "codebook": int(cb_L),
+            },
+            "chr": {
+                "tns_coeffs": np.asarray(chr_tns_coeffs, dtype=np.float64),
+                "T": np.asarray(T_R, dtype=np.float64),
+                "G": G_Rn,
+                "sfc": sfc_R_stream,
+                "stream": mdct_R_stream,
+                "codebook": int(cb_R),
+            },
+        }
+        aac_seq.append(frame_out)
+
+        # Update psycho history (shift register)
+        prev2_L = prev1_L
+        prev1_L = frame_L
+        prev2_R = prev1_R
+        prev1_R = frame_R
+
+        prev_frame_type = frame_type
+
+    # Optional: store to .mat for the assignment wrapper
+    if filename_aac_coded is not None:
+        filename_aac_coded = Path(filename_aac_coded)
+        savemat(
+            str(filename_aac_coded),
+            {"aac_seq_3": np.array(aac_seq, dtype=object)},
+            do_compression=True,
+        )
+
+    return aac_seq
+

source/level_2/core/aac_decoder.py

@@ -22,9 +22,22 @@ import soundfile as sf
 
 from core.aac_filterbank import aac_i_filter_bank
 from core.aac_tns import aac_i_tns
+from core.aac_quantizer import aac_i_quantizer
+from core.aac_huffman import aac_decode_huff
+from core.aac_utils import get_table, band_limits
+from material.huff_utils import load_LUT
 from core.aac_types import *
 
 
+# -----------------------------------------------------------------------------
+# Helper for NB
+# -----------------------------------------------------------------------------
+def _nbands(frame_type: FrameType) -> int:
+    table, _ = get_table(frame_type)
+    wlow, _whigh, _bval, _qthr_db = band_limits(table)
+    return int(len(wlow))
+
+
 # -----------------------------------------------------------------------------
 # Public helpers
 # -----------------------------------------------------------------------------
@@ -252,3 +265,144 @@ def aac_decoder_2(aac_seq_2: AACSeq2, filename_out: Union[str, Path]) -> StereoS
 
     sf.write(str(filename_out), y, 48000)
     return y
+
+
+
+def aac_decoder_3(aac_seq_3: AACSeq3, filename_out: Union[str, Path]) -> StereoSignal:
+    """
+    Level-3 AAC decoder (inverse of aac_coder_3).
+
+    Steps per frame:
+    - Huffman decode scalefactors (sfc) using codebook 11
+    - Huffman decode MDCT symbols (stream) using stored codebook
+    - iQuantizer -> MDCT coefficients after TNS
+    - iTNS using stored predictor coefficients
+    - IMDCT filterbank -> time domain
+    - Overlap-add, remove padding, write WAV
+
+    Parameters
+    ----------
+    aac_seq_3 : AACSeq3
+        Encoded sequence as produced by aac_coder_3.
+    filename_out : Union[str, Path]
+        Output WAV filename.
+
+    Returns
+    -------
+    StereoSignal
+        Decoded audio samples (time-domain), stereo, shape (N, 2), dtype float64.
+    """
+    filename_out = Path(filename_out)
+
+    hop = 1024
+    win = 2048
+    K = len(aac_seq_3)
+
+    if K <= 0:
+        raise ValueError("aac_seq_3 must contain at least one frame.")
+
+    # Load Huffman LUTs once.
+    huff_LUT_list = load_LUT()
+
+    n_pad = (K - 1) * hop + win
+    y_pad = np.zeros((n_pad, 2), dtype=np.float64)
+
+    for i, fr in enumerate(aac_seq_3):
+        frame_type: FrameType = fr["frame_type"]
+        win_type: WinType = fr["win_type"]
+
+        NB = _nbands(frame_type)
+        # We store G separately, so Huffman stream contains only (NB-1) DPCM differences.
+        sfc_len = (NB - 1) * (8 if frame_type == "ESH" else 1)
+
+        # -------------------------
+        # Left channel
+        # -------------------------
+        tns_L = np.asarray(fr["chl"]["tns_coeffs"], dtype=np.float64)
+        G_L = fr["chl"]["G"]
+        sfc_bits_L = fr["chl"]["sfc"]
+        mdct_bits_L = fr["chl"]["stream"]
+        cb_L = int(fr["chl"]["codebook"])
+
+        sfc_dec_L = aac_decode_huff(sfc_bits_L, 11, huff_LUT_list)[:sfc_len].astype(np.int64, copy=False)
+        if frame_type == "ESH":
+            sfc_dpcm_L = sfc_dec_L.reshape(NB - 1, 8, order="F")
+            sfc_L = np.zeros((NB, 8), dtype=np.int64)
+            Gv = np.asarray(G_L, dtype=np.float64).reshape(1, 8)
+            sfc_L[0, :] = Gv[0, :].astype(np.int64)
+            sfc_L[1:, :] = sfc_dpcm_L
+        else:
+            sfc_dpcm_L = sfc_dec_L.reshape(NB - 1, 1, order="F")
+            sfc_L = np.zeros((NB, 1), dtype=np.int64)
+            sfc_L[0, 0] = int(float(G_L))
+            sfc_L[1:, :] = sfc_dpcm_L
+
+        # MDCT symbols: codebook 0 means "all-zero section"
+        if cb_L == 0:
+            S_dec_L = np.zeros((1024,), dtype=np.int64)
+        else:
+            S_tmp_L = aac_decode_huff(mdct_bits_L, cb_L, huff_LUT_list).astype(np.int64, copy=False)
+
+            # Tuple coding may produce extra trailing symbols; caller knows the true length (1024).
+            # Also guard against short outputs by zero-padding.
+            if S_tmp_L.size < 1024:
+                S_dec_L = np.zeros((1024,), dtype=np.int64)
+                S_dec_L[: S_tmp_L.size] = S_tmp_L
+            else:
+                S_dec_L = S_tmp_L[:1024]
+
+        S_L = S_dec_L.reshape(1024, 1)
+
+        Xq_L = aac_i_quantizer(S_L, sfc_L, G_L, frame_type)
+        X_L = aac_i_tns(Xq_L, frame_type, tns_L)
+
+        # -------------------------
+        # Right channel
+        # -------------------------
+        tns_R = np.asarray(fr["chr"]["tns_coeffs"], dtype=np.float64)
+        G_R = fr["chr"]["G"]
+        sfc_bits_R = fr["chr"]["sfc"]
+        mdct_bits_R = fr["chr"]["stream"]
+        cb_R = int(fr["chr"]["codebook"])
+
+        sfc_dec_R = aac_decode_huff(sfc_bits_R, 11, huff_LUT_list)[:sfc_len].astype(np.int64, copy=False)
+        if frame_type == "ESH":
+            sfc_dpcm_R = sfc_dec_R.reshape(NB - 1, 8, order="F")
+            sfc_R = np.zeros((NB, 8), dtype=np.int64)
+            Gv = np.asarray(G_R, dtype=np.float64).reshape(1, 8)
+            sfc_R[0, :] = Gv[0, :].astype(np.int64)
+            sfc_R[1:, :] = sfc_dpcm_R
+        else:
+            sfc_dpcm_R = sfc_dec_R.reshape(NB - 1, 1, order="F")
+            sfc_R = np.zeros((NB, 1), dtype=np.int64)
+            sfc_R[0, 0] = int(float(G_R))
+            sfc_R[1:, :] = sfc_dpcm_R
+
+        if cb_R == 0:
+            S_dec_R = np.zeros((1024,), dtype=np.int64)
+        else:
+            S_tmp_R = aac_decode_huff(mdct_bits_R, cb_R, huff_LUT_list).astype(np.int64, copy=False)
+
+            if S_tmp_R.size < 1024:
+                S_dec_R = np.zeros((1024,), dtype=np.int64)
+                S_dec_R[: S_tmp_R.size] = S_tmp_R
+            else:
+                S_dec_R = S_tmp_R[:1024]
+
+        S_R = S_dec_R.reshape(1024, 1)
+
+        Xq_R = aac_i_quantizer(S_R, sfc_R, G_R, frame_type)
+        X_R = aac_i_tns(Xq_R, frame_type, tns_R)
+
+        # Re-pack to stereo container and inverse filterbank
+        frame_f = aac_unpack_seq_channels_to_frame_f(frame_type, np.asarray(X_L), np.asarray(X_R))
+        frame_t_hat: FrameT = aac_i_filter_bank(frame_f, frame_type, win_type)
+
+        start = i * hop
+        y_pad[start : start + win, :] += frame_t_hat
+
+    y = aac_remove_padding(y_pad, hop=hop)
+
+    sf.write(str(filename_out), y, 48000)
+    return y
+

source/level_2/core/aac_ssc.py

@@ -176,7 +176,7 @@ def _stereo_merge(ft_l: FrameType, ft_r: FrameType) -> FrameType:
 # Public Function prototypes
 # -----------------------------------------------------------------------------
 
-def aac_SSC(frame_T: FrameT, next_frame_T: FrameT, prev_frame_type: FrameType) -> FrameType:
+def aac_ssc(frame_T: FrameT, next_frame_T: FrameT, prev_frame_type: FrameType) -> FrameType:
     """
     Sequence Segmentation Control (SSC).
 

source/level_2/core/aac_tns.py

@@ -30,9 +30,6 @@ from __future__ import annotations
 from pathlib import Path
 from typing import Tuple
 
-import numpy as np
-from scipy.io import loadmat
-
 from core.aac_utils import load_b219_tables
 from core.aac_configuration import PRED_ORDER, QUANT_STEP, QUANT_MAX
 from core.aac_types import *
@@ -377,7 +374,9 @@ def _tns_one_vector(x: MdctCoeffs) -> tuple[MdctCoeffs, MdctCoeffs]:
     sw = _compute_sw(x)
 
     eps = 1e-12
-    xw = np.where(sw > eps, x / sw, 0.0)
+    xw = np.zeros_like(x, dtype=np.float64)
+    mask = sw > eps
+    np.divide(x, sw, out=xw, where=mask)
 
     a = _lpc_coeffs(xw, PRED_ORDER)
     a_q = _quantize_coeffs(a)

source/level_2/core/aac_types.py

@@ -212,6 +212,42 @@ BandValueArray: TypeAlias = FloatArray
 Per-band psychoacoustic values (e.g. Bark position, thresholds).
 """
 
+
+# Quantizer-related semantic aliases
+
+QuantizedSymbols: TypeAlias = NDArray[np.generic]
+"""
+Quantized MDCT symbols S(k).
+
+Shapes:
+- Always (1024, 1) at the quantizer output (ESH packed to 1024 symbols).
+"""
+
+ScaleFactors: TypeAlias = NDArray[np.generic]
+"""
+DPCM-coded scalefactors sfc(b) = alpha(b) - alpha(b-1).
+
+Shapes:
+- Long frames: (NB, 1)
+- ESH frames: (NB, 8)
+"""
+
+GlobalGain: TypeAlias = float | NDArray[np.generic]
+"""
+Global gain G = alpha(0).
+
+- Long frames: scalar float
+- ESH frames: array shape (1, 8)
+"""
+
+# Huffman semantic aliases
+
+HuffmanBitstream: TypeAlias = str
+"""Huffman-coded bitstream stored as a string of '0'/'1'."""
+
+HuffmanCodebook: TypeAlias = int
+"""Huffman codebook id (e.g., 0..11)."""
+
 # -----------------------------------------------------------------------------
 # Level 1 AAC sequence payload types
 # -----------------------------------------------------------------------------
@@ -299,3 +335,77 @@ Level 2 adds:
 and stores:
 - per-channel "frame_F" after applying TNS.
 """
+
+# -----------------------------------------------------------------------------
+# Level 3 AAC sequence payload types (Quantizer + Huffman)
+# -----------------------------------------------------------------------------
+
+class AACChannelFrameF3(TypedDict):
+    """
+    Per-channel payload for aac_seq_3[i]["chl"] or ["chr"] (Level 3).
+
+    Keys
+    ----
+    tns_coeffs:
+        Quantized TNS predictor coefficients for ONE channel.
+        Shapes:
+        - ESH: (PRED_ORDER, 8)
+        - else: (PRED_ORDER, 1)
+
+    T:
+        Psychoacoustic thresholds per band.
+        Shapes:
+        - ESH: (NB, 8)
+        - else: (NB, 1)
+        Note: Stored for completeness / debugging; not entropy-coded.
+
+    G:
+        Quantized global gains.
+        Shapes:
+        - ESH: (1, 8)  (one per short subframe)
+        - else: scalar (or compatible np scalar)
+
+    sfc:
+        Huffman-coded scalefactor differences (DPCM sequence).
+
+    stream:
+        Huffman-coded MDCT quantized symbols S(k) (packed to 1024 symbols).
+
+    codebook:
+        Huffman codebook id used for MDCT symbols (stream).
+        (Scalefactors typically use fixed codebook 11 and do not need to store it.)
+    """
+    tns_coeffs: TnsCoeffs
+    T: FloatArray
+    G: FloatArray | float
+    sfc: HuffmanBitstream
+    stream: HuffmanBitstream
+    codebook: HuffmanCodebook
+
+
+class AACSeq3Frame(TypedDict):
+    """
+    One frame dictionary element of aac_seq_3 (Level 3).
+    """
+    frame_type: FrameType
+    win_type: WinType
+    chl: AACChannelFrameF3
+    chr: AACChannelFrameF3
+
+
+AACSeq3: TypeAlias = List[AACSeq3Frame]
+"""
+AAC sequence for Level 3:
+List of length K (K = number of frames).
+
+Each element is a dict with keys:
+- "frame_type", "win_type", "chl", "chr"
+
+Level 3 adds (per channel):
+- "tns_coeffs"
+- "T" thresholds (not entropy-coded)
+- "G" global gain(s)
+- "sfc" Huffman-coded scalefactor differences
+- "stream" Huffman-coded MDCT quantized symbols
+- "codebook" Huffman codebook for MDCT symbols
+"""

source/level_2/material/huff_utils.py

@@ -1,400 +0,0 @@
-import numpy as np
-import scipy.io as sio
-import os
-
-# ------------------ LOAD LUT ------------------
-
-def load_LUT(mat_filename=None):
-    """
-    Loads the list of Huffman Codebooks (LUTs)
-
-    Returns:
-        huffLUT : list (index 1..11 used, index 0 unused)
-    """
-    if mat_filename is None:
-        current_dir = os.path.dirname(os.path.abspath(__file__))
-        mat_filename = os.path.join(current_dir, "huffCodebooks.mat")
-
-    mat = sio.loadmat(mat_filename)
-
-
-    huffCodebooks_raw = mat['huffCodebooks'].squeeze()
-
-    huffCodebooks = []
-    for i in range(11):
-        huffCodebooks.append(np.array(huffCodebooks_raw[i]))
-
-    # Build inverse VLC tables
-    invTable = [None] * 11
-
-    for i in range(11):
-        h = huffCodebooks[i][:, 2].astype(int)       # column 3
-        hlength = huffCodebooks[i][:, 1].astype(int) # column 2
-
-        hbin = []
-        for j in range(len(h)):
-            hbin.append(format(h[j], f'0{hlength[j]}b'))
-
-        invTable[i] = vlc_table(hbin)
-
-    # Build Huffman LUT dicts
-    huffLUT = [None] * 12  # index 0 unused
-    params = [
-        (4, 1, True),
-        (4, 1, True),
-        (4, 2, False),
-        (4, 2, False),
-        (2, 4, True),
-        (2, 4, True),
-        (2, 7, False),
-        (2, 7, False),
-        (2, 12, False),
-        (2, 12, False),
-        (2, 16, False),
-    ]
-
-    for i, (nTupleSize, maxAbs, signed) in enumerate(params, start=1):
-        huffLUT[i] = {
-            'LUT': huffCodebooks[i-1],
-            'invTable': invTable[i-1],
-            'codebook': i,
-            'nTupleSize': nTupleSize,
-            'maxAbsCodeVal': maxAbs,
-            'signedValues': signed
-        }
-
-    return huffLUT
-
-def vlc_table(code_array):
-    """
-    codeArray: list of strings, each string is a Huffman codeword (e.g. '0101')
-    returns:
-        h : NumPy array of shape (num_nodes, 3)
-            columns:
-              [ next_if_0 , next_if_1 , symbol_index ]
-    """
-    h = np.zeros((1, 3), dtype=int)
-
-    for code_index, code in enumerate(code_array, start=1):
-        word = [int(bit) for bit in code]
-        h_index = 0
-
-        for bit in word:
-            k = bit
-            next_node = h[h_index, k]
-            if next_node == 0:
-                h = np.vstack([h, [0, 0, 0]])
-                new_index = h.shape[0] - 1
-                h[h_index, k] = new_index
-                h_index = new_index
-            else:
-                h_index = next_node
-
-        h[h_index, 2] = code_index
-
-    return h
-
-# ------------------ ENCODE ------------------
-
-def encode_huff(coeff_sec, huff_LUT_list, force_codebook = None):
-    """
-    Huffman-encode a sequence of quantized coefficients.
-
-    This function selects the appropriate Huffman codebook based on the
-    maximum absolute value of the input coefficients, encodes the coefficients
-    into a binary Huffman bitstream, and returns both the bitstream and the
-    selected codebook index.
-
-    This is the Python equivalent of the MATLAB `encodeHuff.m` function used
-    in audio/image coding (e.g., scale factor band encoding). The input
-    coefficient sequence is grouped into fixed-size tuples as defined by
-    the chosen Huffman LUT. Zero-padding may be applied internally.
-
-    Parameters
-    ----------
-    coeff_sec : array_like of int
-        1-D array of quantized integer coefficients to encode.
-        Typically corresponds to a "section" or scale-factor band.
-
-    huff_LUT_list : list
-        List of Huffman lookup-table dictionaries as returned by `loadLUT()`.
-        Index 1..11 correspond to valid Huffman codebooks.
-        Index 0 is unused.
-
-    Returns
-    -------
-    huffSec : str
-        Huffman-encoded bitstream represented as a string of '0' and '1'
-        characters.
-
-    huffCodebook : int
-        Index (1..11) of the Huffman codebook used for encoding.
-        A value of 0 indicates a special all-zero section.
-    """
-    if force_codebook is not None:
-            return huff_LUT_code_1(huff_LUT_list[force_codebook], coeff_sec)
-    
-    maxAbsVal = np.max(np.abs(coeff_sec))
-
-    if maxAbsVal == 0:
-        huffCodebook = 0
-        huffSec = huff_LUT_code_0()
-
-    elif maxAbsVal == 1:
-        candidates = [1, 2]
-        huffSec1 = huff_LUT_code_1(huff_LUT_list[candidates[0]], coeff_sec)
-        huffSec2 = huff_LUT_code_1(huff_LUT_list[candidates[1]], coeff_sec)
-        if len(huffSec1) <= len(huffSec2):
-            huffSec = huffSec1
-            huffCodebook = candidates[0]
-        else:
-            huffSec = huffSec2
-            huffCodebook = candidates[1]
-
-    elif maxAbsVal == 2:
-        candidates = [3, 4]
-        huffSec1 = huff_LUT_code_1(huff_LUT_list[candidates[0]], coeff_sec)
-        huffSec2 = huff_LUT_code_1(huff_LUT_list[candidates[1]], coeff_sec)
-        if len(huffSec1) <= len(huffSec2):
-            huffSec = huffSec1
-            huffCodebook = candidates[0]
-        else:
-            huffSec = huffSec2
-            huffCodebook = candidates[1]
-
-    elif maxAbsVal in (3, 4):
-        candidates = [5, 6]
-        huffSec1 = huff_LUT_code_1(huff_LUT_list[candidates[0]], coeff_sec)
-        huffSec2 = huff_LUT_code_1(huff_LUT_list[candidates[1]], coeff_sec)
-        if len(huffSec1) <= len(huffSec2):
-            huffSec = huffSec1
-            huffCodebook = candidates[0]
-        else:
-            huffSec = huffSec2
-            huffCodebook = candidates[1]
-
-    elif maxAbsVal in (5, 6, 7):
-        candidates = [7, 8]
-        huffSec1 = huff_LUT_code_1(huff_LUT_list[candidates[0]], coeff_sec)
-        huffSec2 = huff_LUT_code_1(huff_LUT_list[candidates[1]], coeff_sec)
-        if len(huffSec1) <= len(huffSec2):
-            huffSec = huffSec1
-            huffCodebook = candidates[0]
-        else:
-            huffSec = huffSec2
-            huffCodebook = candidates[1]
-
-    elif maxAbsVal in (8, 9, 10, 11, 12):
-        candidates = [9, 10]
-        huffSec1 = huff_LUT_code_1(huff_LUT_list[candidates[0]], coeff_sec)
-        huffSec2 = huff_LUT_code_1(huff_LUT_list[candidates[1]], coeff_sec)
-        if len(huffSec1) <= len(huffSec2):
-            huffSec = huffSec1
-            huffCodebook = candidates[0]
-        else:
-            huffSec = huffSec2
-            huffCodebook = candidates[1]
-
-    elif maxAbsVal in (13, 14, 15):
-        huffCodebook = 11
-        huffSec = huff_LUT_code_1(huff_LUT_list[huffCodebook], coeff_sec)
-
-    else:
-        huffCodebook = 11
-        huffSec = huff_LUT_code_ESC(huff_LUT_list[huffCodebook], coeff_sec)
-
-    return huffSec, huffCodebook
-
-def huff_LUT_code_1(huff_LUT, coeff_sec):
-    LUT = huff_LUT['LUT']
-    nTupleSize = huff_LUT['nTupleSize']
-    maxAbsCodeVal = huff_LUT['maxAbsCodeVal']
-    signedValues = huff_LUT['signedValues']
-
-    numTuples = int(np.ceil(len(coeff_sec) / nTupleSize))
-
-    if signedValues:
-        coeff = coeff_sec + maxAbsCodeVal
-        base = 2 * maxAbsCodeVal + 1
-    else:
-        coeff = coeff_sec
-        base = maxAbsCodeVal + 1
-
-    coeffPad = np.zeros(numTuples * nTupleSize, dtype=int)
-    coeffPad[:len(coeff)] = coeff
-
-    huffSec = []
-
-    powers = base ** np.arange(nTupleSize - 1, -1, -1)
-
-    for i in range(numTuples):
-        nTuple = coeffPad[i*nTupleSize:(i+1)*nTupleSize]
-        huffIndex = int(np.abs(nTuple) @ powers)
-
-        hexVal = LUT[huffIndex, 2]
-        huffLen = LUT[huffIndex, 1]
-
-        bits = format(int(hexVal), f'0{int(huffLen)}b')
-
-        if signedValues:
-            huffSec.append(bits)
-        else:
-            signBits = ''.join('1' if v < 0 else '0' for v in nTuple)
-            huffSec.append(bits + signBits)
-
-    return ''.join(huffSec)
-
-def huff_LUT_code_0():
-    return ''
-
-def huff_LUT_code_ESC(huff_LUT, coeff_sec):
-    LUT = huff_LUT['LUT']
-    nTupleSize = huff_LUT['nTupleSize']
-    maxAbsCodeVal = huff_LUT['maxAbsCodeVal']
-
-    numTuples = int(np.ceil(len(coeff_sec) / nTupleSize))
-    base = maxAbsCodeVal + 1
-
-    coeffPad = np.zeros(numTuples * nTupleSize, dtype=int)
-    coeffPad[:len(coeff_sec)] = coeff_sec
-
-    huffSec = []
-    powers = base ** np.arange(nTupleSize - 1, -1, -1)
-
-    for i in range(numTuples):
-        nTuple = coeffPad[i*nTupleSize:(i+1)*nTupleSize]
-
-        lnTuple = nTuple.astype(float)
-        lnTuple[lnTuple == 0] = np.finfo(float).eps
-
-        N4 = np.maximum(0, np.floor(np.log2(np.abs(lnTuple))).astype(int))
-        N = np.maximum(0, N4 - 4)
-        esc = np.abs(nTuple) > 15
-
-        nTupleESC = nTuple.copy()
-        nTupleESC[esc] = np.sign(nTupleESC[esc]) * 16
-
-        huffIndex = int(np.abs(nTupleESC) @ powers)
-
-        hexVal = LUT[huffIndex, 2]
-        huffLen = LUT[huffIndex, 1]
-
-        bits = format(int(hexVal), f'0{int(huffLen)}b')
-
-        escSeq = ''
-        for k in range(nTupleSize):
-            if esc[k]:
-                escSeq += '1' * N[k]
-                escSeq += '0'
-                escSeq += format(abs(nTuple[k]) - (1 << N4[k]), f'0{N4[k]}b')
-
-        signBits = ''.join('1' if v < 0 else '0' for v in nTuple)
-        huffSec.append(bits + signBits + escSeq)
-
-    return ''.join(huffSec)
-
-# ------------------ DECODE ------------------
-
-def decode_huff(huff_sec, huff_LUT):
-    """
-    Decode a Huffman-encoded stream.
-
-    Parameters
-    ----------
-    huff_sec : array-like of int or str
-        Huffman encoded stream as a sequence of 0 and 1 (string or list/array).
-    huff_LUT : dict
-        Huffman lookup table with keys:
-            - 'invTable': inverse table (numpy array)
-            - 'codebook': codebook number
-            - 'nTupleSize': tuple size
-            - 'maxAbsCodeVal': maximum absolute code value
-            - 'signedValues': True/False
-
-    Returns
-    -------
-    decCoeffs : list of int
-        Decoded quantized coefficients.
-    """
-
-    h = huff_LUT['invTable']
-    huffCodebook = huff_LUT['codebook']
-    nTupleSize = huff_LUT['nTupleSize']
-    maxAbsCodeVal = huff_LUT['maxAbsCodeVal']
-    signedValues = huff_LUT['signedValues']
-
-    # Convert string to array of ints
-    if isinstance(huff_sec, str):
-        huff_sec = np.array([int(b) for b in huff_sec])
-
-    eos = False
-    decCoeffs = []
-    streamIndex = 0
-
-    while not eos:
-        wordbit = 0
-        r = 0  # start at root
-
-        # Decode Huffman word using inverse table
-        while True:
-            b = huff_sec[streamIndex + wordbit]
-            wordbit += 1
-            rOld = r
-            r = h[rOld, b]
-            if h[r, 0] == 0 and h[r, 1] == 0:
-                symbolIndex = h[r, 2] - 1  # zero-based
-                streamIndex += wordbit
-                break
-
-        # Decode n-tuple magnitudes
-        if signedValues:
-            base = 2 * maxAbsCodeVal + 1
-            nTupleDec = []
-            tmp = symbolIndex
-            for p in reversed(range(nTupleSize)):
-                val = tmp // (base ** p)
-                nTupleDec.append(val - maxAbsCodeVal)
-                tmp = tmp % (base ** p)
-            nTupleDec = np.array(nTupleDec)
-        else:
-            base = maxAbsCodeVal + 1
-            nTupleDec = []
-            tmp = symbolIndex
-            for p in reversed(range(nTupleSize)):
-                val = tmp // (base ** p)
-                nTupleDec.append(val)
-                tmp = tmp % (base ** p)
-            nTupleDec = np.array(nTupleDec)
-
-            # Apply sign bits
-            nTupleSignBits = huff_sec[streamIndex:streamIndex + nTupleSize]
-            nTupleSign = -(np.sign(nTupleSignBits - 0.5))
-            streamIndex += nTupleSize
-            nTupleDec = nTupleDec * nTupleSign
-
-        # Handle escape sequences
-        escIndex = np.where(np.abs(nTupleDec) == 16)[0]
-        if huffCodebook == 11 and escIndex.size > 0:
-            for idx in escIndex:
-                N = 0
-                b = huff_sec[streamIndex]
-                while b:
-                    N += 1
-                    b = huff_sec[streamIndex + N]
-                streamIndex += N
-                N4 = N + 4
-                escape_word = huff_sec[streamIndex:streamIndex + N4]
-                escape_value = 2 ** N4 + int("".join(map(str, escape_word)), 2)
-                nTupleDec[idx] = escape_value
-                streamIndex += N4 + 1
-            # Apply signs again
-            nTupleDec[escIndex] *= nTupleSign[escIndex]
-
-        decCoeffs.extend(nTupleDec.tolist())
-
-        if streamIndex >= len(huff_sec):
-            eos = True
-
-    return decCoeffs
-    
-

source/pytest.ini

@@ -2,3 +2,6 @@
 pythonpath = .
 testpaths =
     core/tests
+
+filterwarnings =
+    error::RuntimeWarning