diff --git a/vocoder/fregan/stft_loss.py b/vocoder/fregan/stft_loss.py
new file mode 100644
index 0000000..e474474
--- /dev/null
+++ b/vocoder/fregan/stft_loss.py
@@ -0,0 +1,136 @@
+# -*- coding: utf-8 -*-
+
+# Copyright 2019 Tomoki Hayashi
+#  MIT License (https://opensource.org/licenses/MIT)
+
+"""STFT-based Loss modules."""
+
+import torch
+import torch.nn.functional as F
+
+
+def stft(x, fft_size, hop_size, win_length, window):
+    """Perform STFT and convert to magnitude spectrogram.
+    Args:
+        x (Tensor): Input signal tensor (B, T).
+        fft_size (int): FFT size.
+        hop_size (int): Hop size.
+        win_length (int): Window length.
+        window (str): Window function type.
+    Returns:
+        Tensor: Magnitude spectrogram (B, #frames, fft_size // 2 + 1).
+    """
+    x_stft = torch.stft(x, fft_size, hop_size, win_length, window)
+    real = x_stft[..., 0]
+    imag = x_stft[..., 1]
+
+    # NOTE(kan-bayashi): clamp is needed to avoid nan or inf
+    return torch.sqrt(torch.clamp(real ** 2 + imag ** 2, min=1e-7)).transpose(2, 1)
+
+
+class SpectralConvergengeLoss(torch.nn.Module):
+    """Spectral convergence loss module."""
+
+    def __init__(self):
+        """Initilize spectral convergence loss module."""
+        super(SpectralConvergengeLoss, self).__init__()
+
+    def forward(self, x_mag, y_mag):
+        """Calculate forward propagation.
+        Args:
+            x_mag (Tensor): Magnitude spectrogram of predicted signal (B, #frames, #freq_bins).
+            y_mag (Tensor): Magnitude spectrogram of groundtruth signal (B, #frames, #freq_bins).
+        Returns:
+            Tensor: Spectral convergence loss value.
+        """
+        return torch.norm(y_mag - x_mag, p="fro") / torch.norm(y_mag, p="fro")
+
+
+class LogSTFTMagnitudeLoss(torch.nn.Module):
+    """Log STFT magnitude loss module."""
+
+    def __init__(self):
+        """Initilize los STFT magnitude loss module."""
+        super(LogSTFTMagnitudeLoss, self).__init__()
+
+    def forward(self, x_mag, y_mag):
+        """Calculate forward propagation.
+        Args:
+            x_mag (Tensor): Magnitude spectrogram of predicted signal (B, #frames, #freq_bins).
+            y_mag (Tensor): Magnitude spectrogram of groundtruth signal (B, #frames, #freq_bins).
+        Returns:
+            Tensor: Log STFT magnitude loss value.
+        """
+        return F.l1_loss(torch.log(y_mag), torch.log(x_mag))
+
+
+class STFTLoss(torch.nn.Module):
+    """STFT loss module."""
+
+    def __init__(self, fft_size=1024, shift_size=120, win_length=600, window="hann_window"):
+        """Initialize STFT loss module."""
+        super(STFTLoss, self).__init__()
+        self.fft_size = fft_size
+        self.shift_size = shift_size
+        self.win_length = win_length
+        self.window = getattr(torch, window)(win_length)
+        self.spectral_convergenge_loss = SpectralConvergengeLoss()
+        self.log_stft_magnitude_loss = LogSTFTMagnitudeLoss()
+
+    def forward(self, x, y):
+        """Calculate forward propagation.
+        Args:
+            x (Tensor): Predicted signal (B, T).
+            y (Tensor): Groundtruth signal (B, T).
+        Returns:
+            Tensor: Spectral convergence loss value.
+            Tensor: Log STFT magnitude loss value.
+        """
+        x_mag = stft(x, self.fft_size, self.shift_size, self.win_length, self.window.to(x.get_device()))
+        y_mag = stft(y, self.fft_size, self.shift_size, self.win_length, self.window.to(x.get_device()))
+        sc_loss = self.spectral_convergenge_loss(x_mag, y_mag)
+        mag_loss = self.log_stft_magnitude_loss(x_mag, y_mag)
+
+        return sc_loss, mag_loss
+
+
+class MultiResolutionSTFTLoss(torch.nn.Module):
+    """Multi resolution STFT loss module."""
+
+    def __init__(self,
+                 fft_sizes=[1024, 2048, 512],
+                 hop_sizes=[120, 240, 50],
+                 win_lengths=[600, 1200, 240],
+                 window="hann_window"):
+        """Initialize Multi resolution STFT loss module.
+        Args:
+            fft_sizes (list): List of FFT sizes.
+            hop_sizes (list): List of hop sizes.
+            win_lengths (list): List of window lengths.
+            window (str): Window function type.
+        """
+        super(MultiResolutionSTFTLoss, self).__init__()
+        assert len(fft_sizes) == len(hop_sizes) == len(win_lengths)
+        self.stft_losses = torch.nn.ModuleList()
+        for fs, ss, wl in zip(fft_sizes, hop_sizes, win_lengths):
+            self.stft_losses += [STFTLoss(fs, ss, wl, window)]
+
+    def forward(self, x, y):
+        """Calculate forward propagation.
+        Args:
+            x (Tensor): Predicted signal (B, T).
+            y (Tensor): Groundtruth signal (B, T).
+        Returns:
+            Tensor: Multi resolution spectral convergence loss value.
+            Tensor: Multi resolution log STFT magnitude loss value.
+        """
+        sc_loss = 0.0
+        mag_loss = 0.0
+        for f in self.stft_losses:
+            sc_l, mag_l = f(x, y)
+            sc_loss += sc_l
+            mag_loss += mag_l
+        sc_loss /= len(self.stft_losses)
+        mag_loss /= len(self.stft_losses)
+
+        return sc_loss, mag_loss
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