proper handling for mono inputs

app.py

@@ -50,7 +50,7 @@ def separate_all_stems(audio_file_path: str, model_name: str):
 
     is_mono = signal.num_channels == 1
     if is_mono:
-        signal.audio_data = signal.audio_data.repeat(2, 1)  # [batch, channels, samples]
+        signal.audio_data = signal.audio_data.repeat(1, 2, 1)  # [batch, channels, samples]
         signal._num_channels = 2 
 
     sr = signal.sample_rate