Fix inefficient phase unwrapping (#7)

vocos/heads.py

@@ -54,10 +54,15 @@ def forward(self, x: torch.Tensor) -> torch.Tensor:
         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)
-        phase = torch.atan2(y, x)
-        S = mag * torch.exp(phase * 1j)
+        # 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