Understanding Notes with Zero Velocity

Oct 13, 2025 by wbrum.org 1 views

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When working with MIDI files, it's essential to handle notes with zero velocity correctly to avoid issues with note duration and timing. In this article, we'll explore the problem of suppressing notes with zero velocity in MIDI export and discuss a solution using the midifile library.

Understanding Notes with Zero Velocity

In MIDI, a note with zero velocity is equivalent to a note-off event. However, when a note with zero velocity is encountered, it can lead to two note-off events being added to the MIDI file, which can cause problems with note duration and timing.

The Problem with Current Implementation

The current implementation of MIDI export in Verovio adds a note-off event for each note with zero velocity, resulting in two note-off events for the same note. This can lead to issues with note duration and timing, especially when notes with zero velocity occur at the same pitch and channel as other notes.

Solution: Suppressing Notes with Zero Velocity

To solve this problem, we can modify the MidiFile::addNoteOff function to use the dedicated note-off commands (0x80) instead of the note-on with zero velocity method (0x90). This will ensure that notes with zero velocity are suppressed correctly and do not interfere with the duration of other notes.

Modifying the `MidiFile::addNoteOff` Function

To implement this solution, we need to modify the MidiFile::addNoteOff function to use the dedicated note-off commands (0x80). We can do this by adding an additional release velocity to the addNoteOff function:

MidiEvent* MidiFile::addNoteOff(int aTrack, int aTick, int aChannel, int key, int vel) {
   MidiEvent* me = new MidiEvent;
   me->makeNoteOff(aChannel, key, vel);
   me->tick = aTick;
   m_events[aTrack]->push_back_no_copy(me);
   return me;
}

We can then modify the GenerateMIDIFunctor::VisitNote function to use the modified addNoteOff function:

m_midiFile->addNoteOn(m_midiTrack, startTime * tpq, channel, midiNote.pitch, velocity);
m_midiFile->addNoteOff(m_midiTrack, stopTime * tpq, channel, midiNote.pitch, 0);

This will ensure that notes with zero velocity are suppressed correctly and do not interfere with the duration of other notes.

Benefits of the Solution

The solution we've implemented has several benefits:

Notes with zero velocity are suppressed correctly, avoiding issues with note duration and timing.
The dedicated note-off commands (0x80) are used instead of the note-on with zero velocity method (0x90), ensuring that notes with zero velocity are handled correctly.
The solution is easy to implement and requires minimal changes to the existing code.

Conclusion

In conclusion, suppressing notes with zero velocity in MIDI export is a critical issue that can lead to problems with note duration and timing. By modifying the MidiFile::addNoteOff function to use the dedicated note-off commands (0x80), we can ensure that notes with zero velocity are handled correctly and do not interfere with the duration of other notes. This solution is easy to implement and requires minimal changes to the existing code.

Future Work

While this solution addresses the issue of suppressing notes with zero velocity, there are still some potential issues to consider:

The quasi note-off message could interfere with the duration of a note at the same pitch and channel occurring at the same time or before the silenced note if it sustains across that suppressed note's start time.
The solution may not work correctly in all cases, especially when notes with zero velocity occur at the same pitch and channel as other notes.

To address these issues, we can consider implementing additional features, such as:

Using a more sophisticated algorithm to handle notes with zero velocity, such as one that takes into account the duration of the note and the timing of other notes.
Adding a flag to the MidiFile::addNoteOff function to indicate whether the note-off event should be suppressed or not.

In our previous article, we discussed the issue of suppressing notes with zero velocity in MIDI export and implemented a solution using the midifile library. Here are some frequently asked questions (FAQs) and answers to help you better understand the solution and its implementation.

Q: What is the problem with notes with zero velocity in MIDI export?

A: Notes with zero velocity in MIDI export can lead to two note-off events being added to the MIDI file, which can cause problems with note duration and timing.

Q: How does the solution work?

A: The solution modifies the MidiFile::addNoteOff function to use the dedicated note-off commands (0x80) instead of the note-on with zero velocity method (0x90). This ensures that notes with zero velocity are suppressed correctly and do not interfere with the duration of other notes.

Q: What are the benefits of the solution?

A: The solution has several benefits, including:

Notes with zero velocity are suppressed correctly, avoiding issues with note duration and timing.
The dedicated note-off commands (0x80) are used instead of the note-on with zero velocity method (0x90), ensuring that notes with zero velocity are handled correctly.
The solution is easy to implement and requires minimal changes to the existing code.

Q: What are some potential issues with the solution?

A: Some potential issues with the solution include:

The quasi note-off message could interfere with the duration of a note at the same pitch and channel occurring at the same time or before the silenced note if it sustains across that suppressed note's start time.
The solution may not work correctly in all cases, especially when notes with zero velocity occur at the same pitch and channel as other notes.

Q: How can I implement the solution in my code?

A: To implement the solution in your code, you can follow these steps:

Modify the MidiFile::addNoteOff function to use the dedicated note-off commands (0x80) instead of the note-on with zero velocity method (0x90).
Modify the GenerateMIDIFunctor::VisitNote function to use the modified addNoteOff function.
Test the solution to ensure that it works correctly in your specific use case.

Q: What are some additional features that could be implemented to improve the solution?

A: Some additional features that could be implemented to improve the solution include:

Using a more sophisticated algorithm to handle notes with zero velocity, such as one that takes into account the duration of the note and the timing of other notes.
Adding a flag to the MidiFile::addNoteOff function to indicate whether the note-off event should be suppressed or not.

Q: Where can I find more information about the solution and its implementation?

A: You can find more information about the solution and its implementation in our previous article, which provides a detailed explanation of the issue and the solution.

Conclusion

In conclusion, suppressing notes with zero velocity in MIDI export is a critical issue that can lead to problems with note duration and timing. By modifying the MidiFile::addNoteOff function to use the dedicated note-off commands (0x80), we can ensure that notes with zero velocity are handled correctly and do not interfere with the duration of other notes. We hope that this Q&A article has provided you with a better understanding of the solution and its implementation.