fix bug

funasr/models/frontend/default.py

@@ -102,8 +102,8 @@ class DefaultFrontend(AbsFrontend):
         if input_stft.dim() == 4:
             # h: (B, T, C, F) -> h: (B, T, F)
             if self.training:
-                if self.use_channel == None:
-                    input_stft = input_stft[:, :, 0, :]
+                if self.use_channel is not None:
+                    input_stft = input_stft[:, :, self.use_channel, :]
                 else:
                     # Select 1ch randomly
                     ch = np.random.randint(input_stft.size(2))