In stereo, Insert Mode’s signal path flows from inputs 1&2 to Output 1&2. I/O 3&4 can be used for two mono insert points or one stereo insert. If you’re using the H90 in mono, you should only use I/O 1.
When the H90 is in Dual mode, there are two signal paths; you can see them when you enter the Routing menu. The top signal flow is I/O 1&2 in stereo or I/O 1 in mono. The bottom signal flow is I/O 3&4 in stereo or I/O 3 in mono.
