How to Keep Only the Longest Notes at Specific Note-On Times

[Jenix-Park]

Hello, how have you been?

Thanks to DryWetMIDI, I could easily implement a MIDI reader feature.
Over the past few years, I've encountered many MIDI files from different people and realized there are so many MIDI files composed incorrectly.

For example, overlapping notes with zero lengths.
Because their lengths are zero and they are hidden by longer overlapping notes with the same note-on time, they are easily missed by the authors of those MIDI files.

Thankfully, I could easily filter those notes with this one-line code:
midiFile.RemoveNotes(note => note.Length == 0);

However, I still encounter MIDI files with overlapping notes whose lengths are greater than zero.
Is there a built-in way to keep only the longest note at a specific note-on time?

For instance, if we have four C4 notes with lengths of 10, 100, 1000, and 1000 within the same channel at timestamp 0, I want to remove the 10 and 100 ones and then keep ONLY ONE of the two 1000 notes since they are duplicates.

I want to apply this logic to all notes so that only the longest notes remain within each channel.

Is this possible?
Or can you guide me on how to achieve this in the simplest and most efficient way possible?

Thanks!

[melanchall]

Hi!

Well, if you don't worry about performance, this approach should work:

foreach (var trackChunk in midiFile.GetTrackChunks())
{
    using (var notesManager = trackChunk.ManageNotes())
    {
        var notesGroups = notesManager
            .Objects
            .GroupBy(n => (n.Time, n.NoteNumber, n.Channel));

        foreach (var notesGroup in notesGroups)
        {
            var maxLength = notesGroup.Max(n => n.Length);
            var singleMaxLengthNote = notesGroup.First(n => n.Length == maxLength);

            foreach (var note in notesGroup)
            {
                if (note != singleMaxLengthNote)
                    notesManager.Objects.Remove(note);
            }
        }
    }
}

But be aware this code will work only if overlapping notes start at the same time. Because if they don't, things will be non-deterministic. You can read more here.

Also I probably should think about adding such functionality in the Sanitizer tool. Thank you for interesting case.

[Jenix-Park]

Thanks a lot!
DryWetMIDI just keeps improving—I’m loving it more and more! :)

[melanchall]

Removing notes with a velocity of 0 might cause issues because those events actually represent Note-Off messages, right?

Not quite. Note On events with zero velocity can be treated as Note Off ones (btw you can manage this behavior with DWM). But a note is a pair of Note On and Note Off events. So a note with zero velocity is probably junk indeed in many cases.

[Jenix-Park]

Wow thanks!😃

I assumed DryWetMIDI would automatically treat notes with zero velocity as Note Off events, so I didn’t think I needed to handle them manually. If that’s not the case, could you point me to where I can configure this behavior?

[melanchall]

Yes, if we're talking about reading a MIDI file, DWM treats silent Note On events as Note Off ones. You can control this behavior via ReadingSettings.SilentNoteOnPolicy property of the settings passed to MidiFile.Read methods.

[Jenix-Park]

Thank you for the explanation!