Add a partial implementation of percussion (octave, always on)
Add a partial implementation of percussion (octave, always on)

1) This isn't tied into exact tonewheel frequencies: it assumes
the percussion frequency is (midi freq * 2) for one octave up.

2) Volumes are probably way off with tonewheels at 0.95 and
percussion at 0.05.

3) It's hardcoded to on, fast, and octave.

I routed around the preamp stage too, since it was introducing
some noise. I'll figure that out later.

pteichman/roto,pteichman/roto