[src] _reorder_sources() in OLA compares scaled/windowed frame with u…

…n-scaled/un-windowed frame (asteroid-team#688)

* _reorder_sources() is called on the current and the previous frame. The way it had been coded, the previous frame might have been scaled or windowed already. But to get best results, we probably want to compare to an unscaled, un-windowed version.

* Update asteroid/dsp/overlap_add.py

---------

Co-authored-by: Pariente Manuel <[email protected]>

asteroid/dsp/overlap_add.py

@@ -112,11 +112,14 @@ def ola_forward(self, x):
                 # we determine best perm based on xcorr with previous sources
                 frame = _reorder_sources(frame, out[-1], n_src, self.window_size, self.hop_size)
 
+            out.append(frame)
+
+        # apply windowing/scaling *after* _reorder_sources has been called, inplace.
+        for frame in out:
             if self.use_window:
-                frame = frame * self.window.to(frame)
+                frame *= self.window.to(frame)
             else:
-                frame = frame / (self.window_size / self.hop_size)
-            out.append(frame)
+                frame /= self.window_size / self.hop_size
 
         out = torch.stack(out).reshape(n_chunks, batch * n_src, self.window_size)
         out = out.permute(1, 2, 0)