The Lighting Controller

Can I, and if so, how do I assign 2 channels to the same fader?

We do not exactly understand your question, but it works like this:
- each button in Live can be triggered by only one midi message
- a midi message can be assigned to more than one button in Live

@janawaty,
If you just need to control channel 1 and channel 12 with channel fader 1, you can do it by the dmx patching
1=1+12
John

@ JohnRichards
Oh yes, that's certainly the expected answer.
Thank you !

Thank you very much. "+" is the separator I was looking for.