A piano may be more linear, but is still messy. Learn to play a piece in one key, now play it a semitone higher. Oops.linear
In that sense a single guitar string is linear: if you play something using only one string (and no open strings) you can easily transpose it. In fact, absent open strings you can transpose pieces using multiple strings.
(A guitar sound is very nonlinear, btw, since the shorter the string, the more important become the distortions introduced by the attachments of the string.)
I've heard of some keyboard designs with 31 notes per octave where transposing is indeed just moving your hands a couple of keys up or down the keyboard.
V.


