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vocos/heads.py

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+from typing import Optional
+
+import torch
+from torch import nn
+from torchaudio.functional.functional import _hz_to_mel, _mel_to_hz
+
+from vocos.spectral_ops import IMDCT, ISTFT
+from vocos.modules import symexp
+
+
+class FourierHead(nn.Module):
+    """Base class for inverse fourier modules."""
+
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
+        """
+        Args:
+            x (Tensor): Input tensor of shape (B, L, H), where B is the batch size,
+                        L is the sequence length, and H denotes the model dimension.
+
+        Returns:
+            Tensor: Reconstructed time-domain audio signal of shape (B, T), where T is the length of the output signal.
+        """
+        raise NotImplementedError("Subclasses must implement the forward method.")
+
+
+class ISTFTHead(FourierHead):
+    """
+    ISTFT Head module for predicting STFT complex coefficients.
+
+    Args:
+        dim (int): Hidden dimension of the model.
+        n_fft (int): Size of Fourier transform.
+        hop_length (int): The distance between neighboring sliding window frames, which should align with
+                          the resolution of the input features.
+        padding (str, optional): Type of padding. Options are "center" or "same". Defaults to "same".
+    """
+
+    def __init__(self, dim: int, n_fft: int, hop_length: int, padding: str = "same", ckpt: Optional[str] = None):
+        super().__init__()
+        out_dim = n_fft + 2
+        self.out = torch.nn.Linear(dim, out_dim)
+        self.istft = ISTFT(n_fft=n_fft, hop_length=hop_length, win_length=n_fft, padding=padding)
+        # load the checkpoint if provided
+        if ckpt is not None:
+            params = torch.load(ckpt, map_location="cpu")
+            # find head.out.weight and head.out.bias in the checkpoint
+            out_weight = params["head.out.weight"]
+            out_bias = params["head.out.bias"]
+
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
+        """
+        Forward pass of the ISTFTHead module.
+
+        Args:
+            x (Tensor): Input tensor of shape (B, L, H), where B is the batch size,
+                        L is the sequence length, and H denotes the model dimension.
+
+        Returns:
+            Tensor: Reconstructed time-domain audio signal of shape (B, T), where T is the length of the output signal.
+        """
+        x = self.out(x).transpose(1, 2)
+        mag, p = x.chunk(2, dim=1)
+        mag = torch.exp(mag)
+        mag = torch.clip(mag, max=1e2)  # safeguard to prevent excessively large magnitudes
+        # wrapping happens here. These two lines produce real and imaginary value
+        x = torch.cos(p)
+        y = torch.sin(p)
+        # recalculating phase here does not produce anything new
+        # only costs time
+        # phase = torch.atan2(y, x)
+        # S = mag * torch.exp(phase * 1j)
+        # better directly produce the complex value 
+        S = mag * (x + 1j * y)
+        audio = self.istft(S)
+        return audio
+
+
+class IMDCTSymExpHead(FourierHead):
+    """
+    IMDCT Head module for predicting MDCT coefficients with symmetric exponential function
+
+    Args:
+        dim (int): Hidden dimension of the model.
+        mdct_frame_len (int): Length of the MDCT frame.
+        padding (str, optional): Type of padding. Options are "center" or "same". Defaults to "same".
+        sample_rate (int, optional): The sample rate of the audio. If provided, the last layer will be initialized
+                                     based on perceptual scaling. Defaults to None.
+        clip_audio (bool, optional): Whether to clip the audio output within the range of [-1.0, 1.0]. Defaults to False.
+    """
+
+    def __init__(
+        self,
+        dim: int,
+        mdct_frame_len: int,
+        padding: str = "same",
+        sample_rate: Optional[int] = None,
+        clip_audio: bool = False,
+    ):
+        super().__init__()
+        out_dim = mdct_frame_len // 2
+        self.out = nn.Linear(dim, out_dim)
+        self.imdct = IMDCT(frame_len=mdct_frame_len, padding=padding)
+        self.clip_audio = clip_audio
+
+        if sample_rate is not None:
+            # optionally init the last layer following mel-scale
+            m_max = _hz_to_mel(sample_rate // 2)
+            m_pts = torch.linspace(0, m_max, out_dim)
+            f_pts = _mel_to_hz(m_pts)
+            scale = 1 - (f_pts / f_pts.max())
+
+            with torch.no_grad():
+                self.out.weight.mul_(scale.view(-1, 1))
+
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
+        """
+        Forward pass of the IMDCTSymExpHead module.
+
+        Args:
+            x (Tensor): Input tensor of shape (B, L, H), where B is the batch size,
+                        L is the sequence length, and H denotes the model dimension.
+
+        Returns:
+            Tensor: Reconstructed time-domain audio signal of shape (B, T), where T is the length of the output signal.
+        """
+        x = self.out(x)
+        x = symexp(x)
+        x = torch.clip(x, min=-1e2, max=1e2)  # safeguard to prevent excessively large magnitudes
+        audio = self.imdct(x)
+        if self.clip_audio:
+            audio = torch.clip(x, min=-1.0, max=1.0)
+
+        return audio
+
+
+class IMDCTCosHead(FourierHead):
+    """
+    IMDCT Head module for predicting MDCT coefficients with parametrizing MDCT = exp(m) · cos(p)
+
+    Args:
+        dim (int): Hidden dimension of the model.
+        mdct_frame_len (int): Length of the MDCT frame.
+        padding (str, optional): Type of padding. Options are "center" or "same". Defaults to "same".
+        clip_audio (bool, optional): Whether to clip the audio output within the range of [-1.0, 1.0]. Defaults to False.
+    """
+
+    def __init__(self, dim: int, mdct_frame_len: int, padding: str = "same", clip_audio: bool = False):
+        super().__init__()
+        self.clip_audio = clip_audio
+        self.out = nn.Linear(dim, mdct_frame_len)
+        self.imdct = IMDCT(frame_len=mdct_frame_len, padding=padding)
+
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
+        """
+        Forward pass of the IMDCTCosHead module.
+
+        Args:
+            x (Tensor): Input tensor of shape (B, L, H), where B is the batch size,
+                        L is the sequence length, and H denotes the model dimension.
+
+        Returns:
+            Tensor: Reconstructed time-domain audio signal of shape (B, T), where T is the length of the output signal.
+        """
+        x = self.out(x)
+        m, p = x.chunk(2, dim=2)
+        m = torch.exp(m).clip(max=1e2)  # safeguard to prevent excessively large magnitudes
+        audio = self.imdct(m * torch.cos(p))
+        if self.clip_audio:
+            audio = torch.clip(x, min=-1.0, max=1.0)
+        return audio