When working with a MIDI track: duplicate it, including all MIDI information, instrument and other settings.
Select three pitches, either randomly or by ear.
On the first track, delete all the notes with the chosen pitches.
On the second track, delete all notes except the ones with the chosen pitches.
Subtly change the instrument, effect or other settings on one of the tracks.
Repeat the procedure for every voice in your piece, making new pitch selections and applying different parameter changes for each track.
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