Hello.
Does anyone know what MIDI channels control what in the OP-1? If I wanted to control the keyboard from an external source for example? Is there a map/list anywhere?
Cheers.
There is no direct access to parameters from external MIDI, you have to use the MIDI CC to get access and then assign this to the destination and P-Dest.
For the keyboard an external keyboard can be used via midi and it offers the benefit of velocity sensitivity. Sync settings for MIDI channels then set up.
P.S. The OP-1 Notebook explains this on Section 4 pages 40, 42 and Section 10, Pages 94, 96, 97 
Press shift and Com. Then hold shift and blue to set channel.