Dave’s “Octovator” keyboard.
Here is the basic keyboard in horizontal view. One problem is that you usually only get one octave. If you want to play outside of the default octave a -8va and a +8va button allow you to shift on the fly.
Additional idea: If you are holding a note, and you hit +8va, the note you’re holding doesn’t change, but the keys around it would shift up the octave.
Note to non-musicians: 8va is musical notation for octave. +8va means shift up one octave.
