@sushi thanks for the explanation, i think i am beginning to understand now 🙂. Let’s call Synth B the synthesizer that should be controlled both by LoopA and the sequencer present on Synth A.
For your usecase, you’re trying to record via autoloop recording on a different track and MIDI port than Synth A is connected to, correct? Because otherwise you’d instantly get the MIDI notes emitted by the SYNTH_A sequencer into the autoloop recording?
Do you have a second MIDI keyboard set up for this autoloop recording task, that you could configure as a general MIDI master keyboard, that would even record note data for SYNTH A? In this case, you could avoid the connection back from SYNTH_A to LoopA entirely and avoid the issue (if SYNTH_A has a note forwarding feature as we discussed earlier). Then you could forward LoopA notes to the target synth connected through SYNTH_A. Not every synth has this MIDI IN->OUT forwarding feature, though. But you can emulate this with an external MIDI merger as well:
LoopA -> Synth A
LoopA -> merge IN A -> Synth B
SynthA -> merge IN B -> Synth B
I would recommend to do so, because even if we had a “disable-transposition-with-SELECT” feature in the configuration settings in the future, at one day you might just want to use this keyboard based transposition feature (which is a lot of fun) and it wouldn’t work in this setup. Also you might run into the issue where you would want to record something in a running sequence and would get back sequence data from the also running sequencer built into Synth A - my MIDI cabling suggestion therefore is to separate sequencer outputs and merge them just before the synthesizer which is to be controlled by the sequencers, this allows you to grow your setup and even add more sequencers without any further hassles.
Best regards and have a nice weekend,