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MIDI import only detects overlaps from same start time (rather than same end time also)

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Issue 类型
缺陷
描述清晰度
基本清楚
活跃度
停滞
技术栈
python
领域
backend

调研方向

Start by running the reproduction snippet on the attached repro-src.mid and comparing repro-exported.mid against it. The title points at MIDI import detecting overlaps by shared start time but not shared end time, so check how tied notes are grouped when a bass note joins the chord. Done means the exported file holds the C3/E5 chord through beat one of measure 2 without re-attacking it, and the single-track case matches the multi-track workaround.

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描述

music21 version

9.9.1

Operating System(s) checked
macOS 26.2

Problem summary

In some cases, importing then re-exporting a MIDI file with a note tied across a measure causes the note to repeat.

Steps to reproduce

from music21 import *
f = converter.parse('repro-src.mid')
f.write('midi', "repro-exported.mid")

Where:

  • repro-src.mid is a MIDI type 1 file with a single track, rendering this:
Image

Expected vs. actual behavior

  • Expected: The exported MIDI file represents the same musical intention as the source--that is, the C3/E5 chord is held through the first beat of the 2nd measure.
  • Actual: The exported MIDI file doesn't tie the C3/E5 chord, but rather plays it again at the beginning of the measure, as if it was written:
Image

More information

I've tried multiple variations of this and found a few different behaviors that all seem to be related, but I'm not sure what the actual expected behavior should be given the structure of the source MIDI. Is my program required to "clean up" or parse the MIDI file into separate tracks somehow before having music21 export it?

  • If you show() the file, the score looks even different from the exported MIDI: it plays the A4 notes in series with the C3/E5 chord, not simultaneously
Image
  • If I edit the MIDI file to have the E5 and the A4 notes on one track, and the C3 on a second track (e.g., export the C3 onto a bass clef), everything works as expected. The exported file has 3 tracks, with the E5 and A4 notes on track 2, and the C3 on track 3.
Image
  • If I remove the C3 note so that only the E5 is tied, the export works as expected. It seems like something about adding the bottom note is causing the midi export to be wonky. (Note however that in this case, show() still renders the A4 notes in series with the E5, rather than simultaneously with it.)
Image
  • The MIDI files in question are mechanically generated, so there shouldn't be any question of duration variance causing problems.

I've attached the source and exported MIDI files for context.

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