Any reason not to use a proper DAC or digital potentiometer? At least do yourself a favor by using a PWM DAC. Nowadays MCUs are just dirt cheap.
Well, the conext for this project is to build analog synthesizers, using the "period correct" analog technology. Nothing wrong with that; there are people around here who build Z80 computers...
Not my cup of tea, but there are some pretty cool projects on the musicfromouterspace.com website AnreasF found.
EDIT: One could argue that this project should
not be posted in the "Microcontrollers and FPGAs" section...