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"""
Audio processing tools to convert between spectrogram images and waveforms.
"""
import io
import typing as T
import numpy as np
from PIL import Image
import pydub
from scipy.io import wavfile
import torch
import torchaudio
def wav_bytes_from_spectrogram_image(image: Image.Image) -> T.Tuple[io.BytesIO, float]:
"""
Reconstruct a WAV audio clip from a spectrogram image. Also returns the duration in seconds.
"""
print("Starting reconstruction of WAV from spectrogram image...")
max_volume = 50
power_for_image = 0.25
Sxx = spectrogram_from_image(image, max_volume=max_volume, power_for_image=power_for_image)
sample_rate = 44100 # [Hz]
clip_duration_ms = 10000 # [ms]
bins_per_image = image.height
n_mels = image.width
# FFT parameters
window_duration_ms = 100 # [ms]
padded_duration_ms = 400 # [ms]
step_size_ms = 10 # [ms]
# Derived parameters
num_samples = int(image.width / float(bins_per_image) * clip_duration_ms) * sample_rate
n_fft = int(padded_duration_ms / 1000.0 * sample_rate)
hop_length = int(step_size_ms / 1000.0 * sample_rate)
win_length = int(window_duration_ms / 1000.0 * sample_rate)
print("Computing waveform from spectrogram...")
samples = waveform_from_spectrogram(
Sxx=Sxx,
n_fft=n_fft,
hop_length=hop_length,
win_length=win_length,
num_samples=num_samples,
sample_rate=sample_rate,
mel_scale=True,
n_mels=n_mels,
max_mel_iters=200,
num_griffin_lim_iters=32,
)
print("Writing WAV bytes...")
wav_bytes = io.BytesIO()
wavfile.write(wav_bytes, sample_rate, samples.astype(np.int16))
wav_bytes.seek(0)
duration_s = float(len(samples)) / sample_rate
print("Reconstruction complete.")
return wav_bytes, duration_s
def spectrogram_from_image(
image: Image.Image, max_volume: float = 50, power_for_image: float = 0.25
) -> np.ndarray:
"""
Compute a spectrogram magnitude array from a spectrogram image.
TODO: Add image_from_spectrogram and call this out as the reverse.
"""
print("Converting image to spectrogram...")
# Convert to a numpy array of floats
data = np.array(image).astype(np.float32)
# Flip Y take a single channel
data = data[::-1, :]
# Invert
data = 255 - data
# Rescale to max volume
data = data * max_volume / 255
# Reverse the power curve
data = np.power(data, 1 / power_for_image)
print("Conversion complete.")
return data
def spectrogram_from_waveform(
waveform: np.ndarray,
sample_rate: int,
n_fft: int,
hop_length: int,
win_length: int,
mel_scale: bool = True,
n_mels: int = 512,
) -> np.ndarray:
"""
Compute a spectrogram from a waveform.
"""
print("Computing spectrogram from waveform...")
spectrogram_func = torchaudio.transforms.Spectrogram(
n_fft=n_fft,
power=None,
hop_length=hop_length,
win_length=win_length,
)
waveform_tensor = torch.from_numpy(waveform.astype(np.float32)).reshape(1, -1)
Sxx_complex = spectrogram_func(waveform_tensor).numpy()[0]
Sxx_mag = np.abs(Sxx_complex)
if mel_scale:
mel_scaler = torchaudio.transforms.MelScale(
n_mels=n_mels,
sample_rate=sample_rate,
f_min=0,
f_max=10000,
n_stft=n_fft // 2 + 1,
norm=None,
mel_scale="htk",
)
Sxx_mag = mel_scaler(torch.from_numpy(Sxx_mag)).numpy()
print("Spectrogram computation complete.")
return Sxx_mag
def waveform_from_spectrogram(
Sxx: np.ndarray,
n_fft: int,
hop_length: int,
win_length: int,
num_samples: int,
sample_rate: int,
mel_scale: bool = True,
n_mels: int = 768,
max_mel_iters: int = 200,
num_griffin_lim_iters: int = 32,
device: str = "cpu",
) -> np.ndarray:
"""
Reconstruct a waveform from a spectrogram.
This is an approximate inverse of spectrogram_from_waveform, using the Griffin-Lim algorithm
to approximate the phase.
"""
print("Reconstructing waveform from spectrogram...")
Sxx_torch = torch.from_numpy(Sxx).to(device)
if mel_scale:
mel_inv_scaler = torchaudio.transforms.InverseMelScale(
n_mels=n_mels,
sample_rate=sample_rate,
f_min=0,
f_max=10000,
n_stft=n_fft // 2 + 1,
norm=None,
mel_scale="htk",
).to(device)
Sxx_torch = mel_inv_scaler(Sxx_torch)
griffin_lim = torchaudio.transforms.GriffinLim(
n_fft=n_fft,
win_length=win_length,
hop_length=hop_length,
power=1.0,
n_iter=num_griffin_lim_iters,
).to(device)
waveform = griffin_lim(Sxx_torch).cpu().numpy()
print("Waveform reconstruction complete.")
return waveform
def mp3_bytes_from_wav_bytes(wav_bytes: io.BytesIO) -> io.BytesIO:
print("Converting WAV bytes to MP3 bytes...")
mp3_bytes = io.BytesIO()
sound = pydub.AudioSegment.from_wav(wav_bytes)
sound.export(mp3_bytes, format="mp3")
mp3_bytes.seek(0)
print("Conversion complete.")
return mp3_bytes
def image_from_spectrogram(spectrogram: np.ndarray, max_volume: float = 50, power_for_image: float = 0.25) -> Image.Image:
"""
Compute a spectrogram image from a spectrogram magnitude array.
"""
print("Converting spectrogram to image...")
# Apply the power curve
data = np.power(spectrogram, power_for_image)
# Rescale to 0-255
data = data * 255 / max_volume
# Invert
data = 255 - data
# Convert to a PIL image
image = Image.fromarray(data.astype(np.uint8))
# Flip Y
image = image.transpose(Image.FLIP_TOP_BOTTOM)
# Convert to RGB
image = image.convert("RGB")
print("Conversion complete.")
return image |