TODO

quantise playback speed to rational values
display the playback and harmonics when quantised
multiple grain buffers - TouchOsc interface to select which to send to
play back all buffers?
refactor for multitrack
- which controls are per-track and which are global? sort these out in the UI
- encapsulate a grainstrack in an object?
auto-mix: base the mix level on how loud the incoming signal is so that tracks don't fade out
fancier playback:
- intertwine different rates and directions
rhythm controls
- number of steps in step granulator
- modulate grain level in time with playback
- sync LFOs to playback