It is not exactly clear what it is you are trying to accomplish, but here is what is in play. When connected to a computer via USB, you can have the MONTAGE Tone Generator establish two audio paths for data. The first always exists ... and the second is digital audio.

The USB connection establishes a digital audio path. You can route each Part either to the default Main L/R or assign it to a number USB bus. This is the path that can be recorded in the computer DAW software.

When these two pathways for audio exist, you will hear doubling. The “direct” signal is heard immediately, and a few milliseconds later you will hear the second path. USB signal arrives in the DAW, is time stamped and recorded, then routed back to the MONTAGE acting as Digital-to-Analog converter and then to your Main L/R analog outputs (this is the “latent” signal).

You can choose to *monitor* (listen to) the ‘direct’ signal or the ‘latent‘ signal. You want to avoid listening to both!
The signal on its way to be recorded or the signal post (after) the recorder (DAW).

In most cases you would listen to the direct signal, it is latency free, this way there is no delay whatsoever. You are listening as you normally do when Not recording.

You would listen to the latent signal only when you are additionally processing the signal in the computer with effects... in order to hear what the computer plugin effect is doing, you must wait for the signal to be returned to the MONTAGE and after it has been converted to analog.

This explains how the audio system is setup when using the MONTAGE for A/D and D/A conversion.
You have a choice:
__In the MONTAGE go to [UTILITY] > “Settings” > “Audio I/O” > “Direct Monitor” On/Off
When ON you can see how audio is delivered or not to the Main L/R (Analog Outs).

__In your DAW go to the Audio Track, you can usually find a Record Ready button, a Speaker icon, and a Mute button that allows you determine routing of the signal.

When you want to monitor Direct, you would Mute the Audio Track in your DAW during Record
When you want to listen to just the recording as it happens, you would set “Direct Monitor” = Off in the MONTAGE, and listen to the signal from the Audio Track.

That’s how it is designed to function. Allowing the performer to listen with Zero Latency (direct), or post the signal being processed... it is your choice.
You, and you don’t say why, want to monitor yourself playing Part 1, yet not hear Part 2 which is being sent to the computer.

The reason it is still coming out the Main L/R analog outputs is because it is still being routed there. See the MONTAGE “Audio Signal Flow” diagram. You need to break the connection to the Main L/R Analog Outs. You do so by turning “Direct Monitor” = Off. Now the signal must go Out the USB OUT to the computer... when it is returned to MONTAGE (bottom row) you can see how it is routed to the Analog Outs.

All routing and monitoring setup is done in the software. You don’t say but if it were a DAW with audio record capability, you would create a Stereo Audio Input and Audio Track for Part 1, and a second Stereo Audio Input and Audio Track for Part 2.

Set Audio Track 1 to be monitored (speaker icon active)
Set Audio Track 2 with the Track MUTE active.

You will be monitoring everything ‘post’ the software, and using its ability to route signal to the Outputs or not (Mute).
Part 2 can still be recorded (if that is your goal) you just will not be able to hear it until you play the Track back.

Hope that helps.

BM,
Thanks for your usual highly detailed response. And yes, it was indeed a great help.

The key for me in this was to route *all* parts back to the computer and let the software do the routing. So my setup now has Part 1 routed to USB 1/2 and and Part 2 routed to USB 3/4. Using Logic on a Mac, I was able to route the output of Part 1 back to the Montage and Part 2 to another audio output device.

Just FYI, this is what I am trying to achieve. It is something that could more easily be done by routing the individual assignable outputs, but I already have those outputs designated for another purpose.

I have recently bought a vocal harmonizer unit for guitar players. It automatically adds harmonies to your vocals and uses a *clean* guitar signal to figure out the key your are playing. The unit is normally connected directly to a guitar to get the clean signal and the thru from the unit is connected to the pedals etc.

I wanted to get this unit working with the Montage but the documentation says that it doesn't like signals from synths - it wants a clean guitar signal to work out the key.

So my idea was to create a specific part in my performance with a montage clean guitar sound and to use the scenario I described to route the clean guitar to a second USB audio interface I have attached to my Mac. The part will never be heard as the output signal from the second USB audio device goes directly into the vocal harmoniser to feed it the notes it expects.

So with your help, this scenario does work. The vocal harmoniser is still in the post though. So need to wait to try it all fully 🙂

As I said, this would probably be better suited to using the assignable outputs as I could take my computer out of the scenario altogether. So I may rethink my set up with that in mind.

Thanks again for your assistance
Sean