Am I missing something in the manual? If I drop the level of Fader 1, then both the volume of Part 1 and the A/D input goes down.

That is not the case in normal routing scenarios. If you drop the level of the "Master Volume" slider, both the volume of the A/D Input and all Montage Parts will be reduced. Faders 1-8 are exclusively used for volumes for Parts 1-8, or Parts 9-16, or Elements/Operators 1-8. They can never be assigned to control the volume of the A/D Input directly.

However, if I go to the mixer page, I can select the volume of Part 1, drop it to zero and the A/D input will still be audible.

Each Part has its own fader icon on the mixer screen, including the analog-to-digital in and the digital (USB) in channels.

Is it possible to unlink the A/D input level from Fader 1 or Part 1? Or to assign the A/D input to a different fader?

Fact is they cannot really be linked, and the A/D Input can never be controlled by a FADER 1-8.

That said, in routing the signal of the A/D Input through the Montage Motion Control Synthesis Engine, you might send it in as a source to a Vocoder assigned to a Part; In this case the encoded signal can be controlled using the Fader. Technically, that is not the A/D signal, at that point, it is the result of the A/D signal encoded and shaping the synth Part. The Dry Level signal (mic clean signal) is routed through the system separately. You don't mention anything about the Vocoder or any Side Chaining options that are available to the A/D Input in your question. But in normal routing scenarios the A/D Input has its own channel screen, and will not have access to any of the numbered Faders, unless you are using the A/D input as a modifying source within the Motion Control engine.

Let us know.

No, I'm not using a vocoder.

On every single preset Live Set or Performance I choose, Fader 1 also controls the A/D input volume.

Should I do a factory reset?

I'm running OS 1.20.4. I tried Initialize all Data, Initialize All Settings and Initialize Advanced Settings. Still the same behaviour.

Can you please try this on yours?

What do you have plugged into the A/D Input?
If it is a MIDI device that you are also connected to via MIDI (either directly or through a computer or other smart device) remember FADER 1 can send cc7 Out via MIDI. This would be controlling the volume of the device, not the A/D Input volume.

Bingo! MIDI CC7 was the culprit. I had an Access Virus connected to it.

I was confused because on the Audio & Part Mixing page, selecting Part 1 volume and dropping it with the Data encoder reduces the part volume AND also the Fader leds. However this doesn't send MIDI CC7, only moving the fader does.

Thanks again for the clarification.

In general, when creating a Zone control for an external device you may find it convenient to create a separate Part. This way your internal and external Parts have their own FADER. Think of the Montage as being able to control 8 Parts. Those eight can be a combination of internal and external Parts.

For example, say you are playing four internal Parts (CFX Concert), ADD (+) a fifth Part for your external device, set its Zone Switch On, set the INT SW to Off, (this designates it as an external Part).