Added an exception

audio.py

@@ -33,7 +33,7 @@ _SCALING_FACTORS = pd.Series(
 def midi_to_notes(midi_file: str) -> pd.DataFrame:
   """
   Convert midi file to "song map" (dataframe where each note is broken
-  into its components).
+  into its components). The song must have at least 3501 notes.
 
   Parameters
   ----------
@@ -53,6 +53,10 @@ def midi_to_notes(midi_file: str) -> pd.DataFrame:
 
   # Sort the notes by start time
   sorted_notes = sorted(instrument.notes, key=lambda note: note.start)
+
+  if len(sorted_notes) < 3501:
+      raise ValueError("Song must have at least 3501 notes.")
+    
   prev_start = sorted_notes[0].start
 
   # Separate each individual note in pitch, step and duration