One goal I have for the Bucky Glow is to produce both audio and MIDI signals. I recently read this article on producing more complex sounds with Arduino. It works great! However, it is still a challenge to produce high quality sounds quickly. The more complex the audio signal, the more frequency components required and the longer it takes to update the signal.
I set up capacitive touch sensors and a toggle switch to flip between audio and MIDI signals. I used my favorite MIDI library and this great article on Arduino and audio signals. Next step is to produce better sounding audio signals that are fast enough to couple with an instrument.