Were you going to make an instructable for this?

Looks and sounds interesting, can't really tell from the video, but it seems your pitch knob is a standard knob, not numerated (as with amplifiers, guitars, etc.) maybe using one that's numbered would help in more accurately dialing in pitches to achieve a less randomized sound. That is, you could assign a 1-value to your lowest pitch, and know that its maybe a low C (or whatever) and then know at which point you reach the next octave (wherever that may be, 4? 6? midway between two numbers...). In this way you could accurately shoot those pitch changes up and down octaves instead of just lightly spinning the knob with finger taps til you find something that sounds ok. The numeric value would just make it easier (as is the case between a fretless bass vs. a fretted one)

OK... nice work, but how about an instructable teaching us exactly how you modded your gameboy?