I recorded my grandfather (88 years old) singing some family songs, and want to now add background music. Problem is that some of his singing is slightly off tune (to within half a note). Instead of tuning his voice - which I think would take away from his personality - I want to detune the piano accompaniment. I've already laid the tracks and now want to add the gradual detuning - but can't work out what the MIDI controller number is. I'm using a Yamaha Tyros. Anyone?

While we're at it, where can I get a full list of Yamahas MIDI controller number protocol?

Thanks, Chony.