Kyle writes –

A friend of mine wanted a bitcrusher/samplerate reducer pedal for his guitar — I thought “you could probably do that with an Arduino”. The quality turned out surprisingly reasonable. I’ve released the code, which sets up the pins on an Arduino for doing 10-bit DSP at reasonable sample rates

The design includes bitcrush, bitshift, and overdrive effects – very cool. Check out the instructable for all the details – Lo Fi Arduino Guitar Pedal