Percussion "pitch" not preserved on MIDI import for generic/unrecognized percussion instruments

[leleogere]

music21 version

9.1.0

Problem summary

I'm trying to manipulate a MIDI file from the Groove MIDI dataset:
groove/drummer1/eval_session/1_funk-groove1_138_beat_4-4.mid

When I read, and then immediately rewrite the file on the disk, some "pitches" (or rather some instruments as drums are represented as pitches in channel 9/10 in midi) are changed.

Steps to reproduce

Run the following:

from pathlib import Path
import music21

file_path = Path("groove/drummer1/eval_session/1_funk-groove1_138_beat_4-4.mid")

stream = music21.converter.parse(file_path, quantizePost=False)
stream.write("midi", fp="/tmp/test_write.mid")

Then open both the original and the new file in a MIDI editor:

Expected vs. actual behavior

I would expect the new file to be the same as the initial one.

More information

Python version: 3.11.5

[jacobtylerwalls]

Thanks for the report.

It boils down to music21 exhibiting a lossy import for percussion sounds it has decided not represent with dedicated classes (along the lines of #1518). We could still preserve the pitch number from the MIDI event and stick it here, where you see None currently:

>>> # s = converter.parse(...
>>> [(n.storedInstrument, n.storedInstrument.percMapPitch) for n in s["PercussionChord"].first().notes]
[
(<music21.instrument.UnpitchedPercussion 'Percussion'>, None),
(<music21.instrument.UnpitchedPercussion 'Percussion'>, None),
(<music21.instrument.BassDrum 'Bass Drum'>, 36)
]