Also to add. This device does not actually have any audio involved. It controls say the pitch of the audio or the rate of an lfo in the modulation of the audio. So it's all DC right? Not sure if this matter.
The synth operates at -5 to +5
After the Arduino it gets put into an attenuverter which attenuates and inverts the 5v signal from the Arduino. Back to -5v to +5v. Then goes back to the synth for control.
When an Arduino outputs a voltage it only has a granularity of numbers 0 to 255 to represent voltages 0 to 5V.
... but even for that we need at least an RC-filter.
This is just something I started a few weeks ago because I need a controller that is not available on the consumer market.
I am assuming that if I swap the pot for a jack for a control voltage. It should work.