In via Tom McClintock. Interesting. Title link takes you to a site hosting the virtual 2A03 Synth. The 2A03 was the synth chip used in the Nintendo NES.

"For those of you familiar with the 8-bit music scene, the 2A03 was the integrated circuit at the heart of the old Nintendo Entertainment System. The 2A03 was a custom IC containing, among other things, a 6502 processor and audio generator circuits. These circuits are what gave the NES it's unique sound."
"It is an 2A03 freed from the limitations of the original hardware. The core 2A03 "sound" howerver is preserved and faithfully reproduced.
At it's core, the 2A03 contains 4 sound generation circuits:
triangle generator
2 square wave generators (each having a slightly different sweep algorithm)
noise generator"