Ethanfel
9c784b4bdb
Spectral-loss-only fine-tuning of the BigVGAN vocoder (mel→waveform)
on BJ audio clips. DiT and VAE are completely frozen. Losses: mel L1
reconstruction + multi-resolution STFT magnitude L1 (same three
resolutions as the BigVGAN discriminator config). Saves in
{'generator': state_dict} format compatible with the original BigVGAN
checkpoint. Loader replaces vocoder weights in the loaded SELVA_MODEL
in-place so no full model reload is needed.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
241 lines
9.9 KiB
Python
241 lines
9.9 KiB
Python
"""SelVA BigVGAN Vocoder Fine-tuner.
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Fine-tunes only the BigVGAN vocoder (mel → waveform) on BJ audio clips using
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spectral reconstruction losses. The DiT and VAE are completely untouched.
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Loss: L1 mel reconstruction + multi-resolution STFT magnitude L1.
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No GAN discriminator — this is a proof-of-concept to verify that the vocoder
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can absorb BJ timbral characteristics before investing in full adversarial training.
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Save format: {'generator': vocoder.state_dict()} — same as the original BigVGAN
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checkpoint so it can be loaded with SelVA BigVGAN Loader.
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"""
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import random
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from pathlib import Path
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import torch
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import torch.nn.functional as F
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import torchaudio
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import comfy.utils
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import folder_paths
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from .utils import SELVA_CATEGORY, get_device, soft_empty_cache
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# Multi-resolution STFT windows — same three resolutions as BigVGAN discriminator config.
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_STFT_RESOLUTIONS = [
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(1024, 120, 600),
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(2048, 240, 1200),
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(512, 50, 240),
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]
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def _stft_mag(wav, n_fft, hop_length, win_length, device):
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"""Magnitude STFT. wav: [B, T] → [B, n_fft//2+1, T']"""
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window = torch.hann_window(win_length, device=device)
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spec = torch.stft(
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wav, n_fft=n_fft, hop_length=hop_length, win_length=win_length,
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window=window, center=True, return_complex=True,
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)
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return spec.abs()
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def _multi_resolution_stft_loss(pred_wav, target_wav, device):
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"""Average L1 mag loss across three STFT resolutions. inputs: [B, 1, T]"""
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pred = pred_wav.squeeze(1) # [B, T]
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target = target_wav.squeeze(1)
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loss = torch.zeros(1, device=device)
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for n_fft, hop, win in _STFT_RESOLUTIONS:
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pm = _stft_mag(pred, n_fft, hop, win, device)
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tm = _stft_mag(target, n_fft, hop, win, device)
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T = min(pm.shape[-1], tm.shape[-1])
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loss = loss + F.l1_loss(pm[..., :T], tm[..., :T])
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return loss / len(_STFT_RESOLUTIONS)
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class SelvaBigvganTrainer:
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OUTPUT_NODE = True
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CATEGORY = SELVA_CATEGORY
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FUNCTION = "train"
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RETURN_TYPES = ("STRING",)
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RETURN_NAMES = ("checkpoint_path",)
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OUTPUT_TOOLTIPS = ("Path to saved vocoder checkpoint — load with SelVA BigVGAN Loader.",)
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DESCRIPTION = (
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"Fine-tunes the BigVGAN vocoder (mel→waveform) on BJ audio clips using "
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"spectral losses (mel L1 + multi-resolution STFT L1). DiT and VAE stay frozen. "
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"16k mode only. Load the result with SelVA BigVGAN Loader."
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)
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@classmethod
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def INPUT_TYPES(cls):
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return {
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"required": {
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"model": ("SELVA_MODEL",),
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"data_dir": ("STRING", {
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"default": "",
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"tooltip": "Directory with BJ audio files (.wav/.flac/.mp3). Searched recursively.",
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}),
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"output_path": ("STRING", {
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"default": "bigvgan_bj.pt",
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"tooltip": "Where to save the fine-tuned vocoder. Relative paths → ComfyUI output dir.",
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}),
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"steps": ("INT", {
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"default": 2000, "min": 100, "max": 50000,
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"tooltip": "Training steps. 1000–2000 is a good first experiment.",
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}),
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"lr": ("FLOAT", {
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"default": 1e-4, "min": 1e-6, "max": 1e-2, "step": 1e-5,
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"tooltip": "Learning rate. BigVGAN default is 1e-4.",
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}),
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"batch_size": ("INT", {"default": 4, "min": 1, "max": 32}),
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"segment_seconds": ("FLOAT", {
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"default": 1.0, "min": 0.25, "max": 4.0, "step": 0.25,
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"tooltip": "Audio segment length per training sample in seconds.",
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}),
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"save_every": ("INT", {"default": 500, "min": 50, "max": 10000}),
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"seed": ("INT", {"default": 42, "min": 0, "max": 0xFFFFFFFF}),
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},
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}
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def train(self, model, data_dir, output_path, steps, lr, batch_size,
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segment_seconds, save_every, seed):
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import traceback
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if model["mode"] != "16k":
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raise NotImplementedError(
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"[BigVGAN] Only 16k mode is supported. "
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"44k uses BigVGANv2 which requires a different training setup."
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)
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device = get_device()
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feature_utils = model["feature_utils"]
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mel_converter = feature_utils.mel_converter
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sample_rate = 16_000
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strategy = model["strategy"]
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# BigVGANVocoder nn.Module — bypass the @inference_mode wrapper on BigVGAN.forward
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vocoder = feature_utils.tod.vocoder.vocoder
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# Resolve paths
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data_dir = Path(data_dir.strip())
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if not data_dir.is_absolute():
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data_dir = Path(folder_paths.models_dir) / data_dir
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if not data_dir.exists():
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raise FileNotFoundError(f"[BigVGAN] data_dir not found: {data_dir}")
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out_path = Path(output_path.strip())
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if not out_path.is_absolute():
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out_path = Path(folder_paths.get_output_directory()) / out_path
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out_path.parent.mkdir(parents=True, exist_ok=True)
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# Find and pre-load audio clips
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segment_samples = int(segment_seconds * sample_rate)
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audio_files = []
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for ext in ("*.wav", "*.flac", "*.mp3", "*.ogg", "*.aac"):
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audio_files.extend(data_dir.rglob(ext))
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if not audio_files:
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raise FileNotFoundError(f"[BigVGAN] No audio files found in {data_dir}")
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print(f"[BigVGAN] Loading {len(audio_files)} audio files...", flush=True)
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clips = []
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for af in audio_files:
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try:
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wav, sr = torchaudio.load(str(af))
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if wav.shape[0] > 1:
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wav = wav.mean(0, keepdim=True)
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if sr != sample_rate:
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wav = torchaudio.functional.resample(wav, sr, sample_rate)
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wav = wav.squeeze(0) # [L]
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if wav.shape[0] >= segment_samples:
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clips.append(wav)
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else:
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print(f" [BigVGAN] Skip {af.name}: shorter than {segment_seconds}s", flush=True)
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except Exception as e:
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print(f" [BigVGAN] Failed {af.name}: {e}", flush=True)
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traceback.print_exc()
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if not clips:
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raise RuntimeError(
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f"[BigVGAN] No usable clips found (need audio >= {segment_seconds}s)"
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)
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print(f"[BigVGAN] {len(clips)} clips ready segment={segment_seconds}s "
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f"steps={steps} lr={lr} batch={batch_size}\n", flush=True)
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if strategy == "offload_to_cpu":
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feature_utils.to(device)
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soft_empty_cache()
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mel_converter.to(device)
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vocoder.requires_grad_(True)
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optimizer = torch.optim.AdamW(vocoder.parameters(), lr=lr, betas=(0.8, 0.99))
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torch.manual_seed(seed)
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random.seed(seed)
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pbar = comfy.utils.ProgressBar(steps)
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try:
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with torch.inference_mode(False):
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with torch.enable_grad():
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vocoder.train()
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for step in range(steps):
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# Sample random batch
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batch = []
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for _ in range(batch_size):
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clip = random.choice(clips)
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start = random.randint(0, clip.shape[0] - segment_samples)
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batch.append(clip[start : start + segment_samples])
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target_flat = torch.stack(batch).to(device) # [B, T]
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target_wav = target_flat.unsqueeze(1) # [B, 1, T]
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# Fixed target mel (no grad needed here)
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with torch.no_grad():
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target_mel = mel_converter(target_flat) # [B, 80, T_mel]
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# Vocoder forward: mel → waveform
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pred_wav = vocoder(target_mel) # [B, 1, T_wav]
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# Align lengths
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T = min(pred_wav.shape[-1], target_wav.shape[-1])
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pred_t = pred_wav[..., :T]
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target_t = target_wav[..., :T]
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# Mel reconstruction loss: mel(pred) vs target_mel
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pred_mel = mel_converter(pred_t.squeeze(1)) # [B, 80, T_mel']
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T_mel = min(pred_mel.shape[-1], target_mel.shape[-1])
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mel_loss = F.l1_loss(pred_mel[..., :T_mel], target_mel[..., :T_mel])
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# Multi-resolution STFT loss
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stft_loss = _multi_resolution_stft_loss(pred_t, target_t, device)
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loss = mel_loss + stft_loss
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optimizer.zero_grad()
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loss.backward()
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torch.nn.utils.clip_grad_norm_(vocoder.parameters(), 1.0)
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optimizer.step()
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pbar.update(1)
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if (step + 1) % max(1, steps // 20) == 0 or step == steps - 1:
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print(f"[BigVGAN] {step+1}/{steps} "
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f"mel={mel_loss.item():.4f} stft={stft_loss.item():.4f} "
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f"total={loss.item():.4f}", flush=True)
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if (step + 1) % save_every == 0 and (step + 1) < steps:
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step_path = out_path.parent / f"{out_path.stem}_step{step+1}{out_path.suffix}"
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torch.save({"generator": vocoder.state_dict()}, str(step_path))
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print(f"[BigVGAN] Checkpoint: {step_path}", flush=True)
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finally:
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vocoder.requires_grad_(False)
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vocoder.eval()
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if strategy == "offload_to_cpu":
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feature_utils.to("cpu")
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soft_empty_cache()
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torch.save({"generator": vocoder.state_dict()}, str(out_path))
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print(f"\n[BigVGAN] Saved: {out_path}", flush=True)
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return (str(out_path),)
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