Scales other than 12-tone equal temperament, mostly. Awhile ago, I built a keyboard instrument with 156 pressure-sensitive keys. It's 5 octaves, 31 notes per

Scales other than 12-tone equal temperament, mostly. Awhile ago, I built a keyboard instrument with 156 pressure-sensitive keys. It's 5 octaves, 31 notes per octave, based on a just-intonation tuning system. Basic sound demo here: https://www.youtube.com/watch?v=Ep52Vh6oAOE https://www.youtube.com/watch?v=Ep52Vh6oAOE The Lumatone has 280 keys. https://www.lumatone.io/ https://www.lumatone.io/ The Tonal Plexus H-Pi is basically a big array of buttons, arranged in 205-tone equal temperament across 6 octaves. That's over 1200 distinct notes. There aren't many of these in existence, but a friend of mine has one. https://hpi.zentral.zone/tonalplexus https://hpi.zentral.zone/tonalplexus For a 12-TET example, one could represent a 6-string guitar with 24 frets as having (24+1) * 6 distinct notes, or 150. Even that is over the limit. It's possible to work around the the limited number of notes by using the one-note-per-channel trick (formalized as MPE); then you're limited to 16 notes of simultaneous polyphony because that's how many channels MIDI has, but you can pitch-bend to exactly the note you want. But then you're using MIDI in a very different way than it's usually intended, and it's hard to do that without making the user experience worse in various ways. MIDI 2.0 could have expanded the number of notes so that (with per-note pitch bend), no one would ever have to use the note-per-channel trick again, but that's not the choice they made.