Thanks for the quick reply !
What is a "control surface"?
Here's an example, it's like a audio mixer, but no actual audio passes through it:
It simply controls software in the computer which actually handles the audio.
I coded the software in this video, now I'd like to take this further with more control over hardware.
Encoders really need interrupts to avoid missing any pulses. 4 encoders will need 8 interrupt pins. No Arduino has 8 external interrupt pins. And, no they can't be multiplexed.
Hmmm....
This is from the Arduino Due page, am I missing something? (As I said I'm a total noobie)
The Arduino Due board has powerful interrupt capabilities that allows you to attach an interrupt function on all available pins. You can directly specify the pin number in attachInterrupt().