Estimation of phase spectrum based on the Griffin-Lim algorithm.

gla.py

"""Griffin-Lim algorithm.

Copyright (C) 2023 by Akira Tamamori

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"""
import librosa
import numpy as np


def gla(amp_spec, cfg, init_spec=None):
    """Estimation of phase spectrum based on the Griffin-Lim algorithm."""
    hop_length = cfg.feature.hop_length
    frame_length = cfg.feature.frame_length
    n_fft = cfg.feature.n_fft
    iter = cfg.feature.gla_iter
    amp_spec = amp_spec.T
    for i in range(iter):
        if i == 0:
            # 初回は乱数で初期化 or 初期位相スペクトルで初期化
            if init_spec is None:
                phase_spec = np.random.rand(*amp_spec.shape)
            else:
                phase_spec = init_spec.T
        else:
            # 振幅スペクトルと推定された位相スペクトルから複素スペクトログラムを復元
            recovered_spec = amp_spec * np.exp(1j * phase_spec)

            # 短時間フーリエ逆変換で音声を復元
            recovered = librosa.istft(
                recovered_spec,
                n_fft=n_fft,
                hop_length=hop_length,
                win_length=frame_length,
            )

            # 復元音声から複素スペクトログラムを再計算
            complex_spec = librosa.stft(
                recovered,
                n_fft=n_fft,
                hop_length=hop_length,
                win_length=frame_length,
            )

            # 初回以降は計算済みの複素スペクトログラムから位相スペクトルを推定
            phase_spec = np.angle(complex_spec)
    return phase_spec