Gain on PC(USB) input?

[Phoebus]

I can’t find anything about this, probably because it’s so obvious.
I’m feeding background tracks from my phone via USB into channel 9/10 of the Model 12. Everything works as expected, I can use equalizer, and fader. But I can’t control gain - that knob has no effect on the signal. Why?
Is there an assumption that the USB signal always is at unity? (It isn’t due to the multi-track recorder I’m using.)
Or did I miss one of the many configuration options?
Thank you!

 

[Logrinn]

The reason is - according to the flow chart in the manual - that the USB return on channels 9 & 10 come after gain and low cut. But before compressor, eq, fader and pan.
In other words the gain knob and low cut won’t affect the signal coming from your phone to the USB input.

 

[Max Relic]

@Phoebus, the signal path is described in the block diagram on page 213 of the OM.

 

[Phoebus]

@Max Relic and @Logrinn, thank you for your replies. I definitely should have checked the signal path before asking this.
I got the Model 12 for a simple purpose- to be able to record multiple outputs of my electronic drum module with the multi-track recorder on my phone via USB. Which works in all the ways I had hoped for.
But I’m now slowly discovering everything else this unit can do and I’m impressed (and overwhelmed)
Anyone venture a guess why they decided to insert the USB post gain?

 

[Phoebus]

Follow-up question (sort of): After having recorded a multi-track song, is it possible to output each track to it’s corresponding USB channel? If I try to get track 1 into my DAW via USB channel 1, there’s nothing there. (If I have live input, it works)

 

[Max Relic]

[QUOTE]
Anyone venture a guess why they decided to insert the USB post gain?
[/QUOTE]

Scope of the Trim or Gain in a preamplifier is to boost or attenuate the input signal so it is presented to the next stage at an optimum level. The input preamplifier stage in the Model 12 is analog, once the Trim/Gain is correctly adjusted the signal can then be converted to digital with the best S/N quality (i.e. using all the bits of the ADC circuit).

 

[Phoebus]

Ah, OK. It would require to go D/A - Gain - A/D which would likely cause signal degradation. And since the information content wouldn’t increase, it wouldn’t benefit the equalizer either. Thanks!

 

[Max Relic]

I'm not sure if I exposed my thoughts well, I'll rephrase it here to be safe. Since the exact input signal level can't be determined in abstract (being it from weak microphone to strong instrument line level) it is passed through a preamplifier stage where it can be adapted to the Model 12 requirements using the Gain control which is analog; then it is converted to digital. It is assumed that signals coming from USB have already a proper level, for this reason there isn't another gain stage in the digital domain (and it would be redundant to the live input). In case of weak USB signal the channel faders can provide an additional 10dB boost.

 

[Phoebus]

You actually did explain it well. But the added details are appreciated!
Any thoughts on the USB out question (can I send a recorded track 1 to USB out channel 1)?
According to the block diagram, any input (live or MTR) should go to Send, which should show up on the corresponding USB channel. But it doesn’t. As soon as I switch from Live to MTR, the USB goes silent while I can hear the track in the headset.

 

[Max Relic]

Follow-up question (sort of): After having recorded a multi-track song, is it possible to output each track to it’s corresponding USB channel? If I try to get track 1 into my DAW via USB channel 1, there’s nothing there. (If I have live input, it works)

IIRC the Live input is always sent to USB (DAW) and the mode switch (Live-PC-MTR) has no influence on it. I suggest you copy the recorded tracks to your DAW, of course accordingly to your workflow.

 

[Phoebus]

Brilliant! Didn’t think of trying that. You are correct, the live input is sent to USB regardless of the Mode switch setting. Just confirmed it.
Track copy it is, then
Thank you again!

 

[Max Relic]

This video gives a good overview of the Model 12, it's 2 years old so latest firmware updates are not covered: