fix: change the sound of instrumental

app.py

@@ -348,7 +348,7 @@ def combine_stems_for_all(input_dir, output_format="mp3"):
         # Load and combine stems
         stems = {name: AudioSegment.from_file(path) for name, path in stem_paths.items()}
 
-        stems["instrumental"] = stems["instrumental"].apply_gain(-15)
+        stems["instrumental"] = stems["instrumental"].apply_gain(-20)
         combined = stems["vocals"].overlay(stems["bass"]).overlay(stems["others"]).overlay(stems["instrumental"])
 
         # Trim silence at the end