Difference input gain on global settings

[PJD]

Hi!

I was wondering if there is a difference between the input gain found in the global settings, and the input gain in the preset settings (the input block).

When testing, I do feel like there is some difference, but my ears might be decieving me.

Is there a proper technical difference with how the 2 function?

[derdoe]

I don’t know if there’s any official info on this, but the the (global) input gain in the I/O settings seems to have some scaling at certain points to optimize signal to noise ratio. So it has some influence on how the analog signal is processed. The input gain in the preset is just a digital gain.

If you want to go down that rabbit hole:
Basically at +9.3dB (and other points) the signal changes and reduces the noise floor.
So some people use this fact to set the global input gain to +9.3dB and the preset input gain to -9.3dB to effectively get a lower noise floor.

Thoroughly confused about gain staging and about to give up

This also improves the noise floor, because something happens/changes in the A/D conversion at +9,3db. You can clearly hear it when slowly turning the global input gain up step by step. Therefore I have my global input gain at +9,3db and the gain on my input blocks at -9,3db. But that doesn’t falsify the above argument of the blocks behaving the most realistic when they see a overall gain of ±0,0db - because that holds true here (+9,3-9,3=0)

Thoroughly confused about gain staging and about to give up

My guess is that it works a bit like the input trim you described, but it’s not continuous. If you just put some high gain amp and a cab on row 1, you can hear the noise floor even without a guitar. From 0 to 9.3dB you turn up the gain and you can hear the noise floor get louder. At 9.3dB, like DavidRSTV described, you can suddenly hear the noise drop. There are more breakpoints like this somewhere around 12+dB and after that. So I think the QC does only increase the gain on the digital side …

[PJD]

Great explanation!

So, now we’re down that rabbit hole anyway, I would like to start experimenting with my input gain, as it’s kind of a game changer (or so i’m told). The ‘correct’ way would then be to put my input gain to a cutoff point (e.g. 9.3 dB), compensate for that within the preset gain. And this results in a higher SNR?

[derdoe]

Yes, that’s the idea.
That said, you should definitely try both ways to compare and decide for yourself if it’s worth the hassle.
For example, if you later change guitars and decide that the input gain needs to be lower, you’d have to touch every preset, because lowering the global input would bring you below 9.3dB.

[ScreamOfAnger]

That’s common practice for preamps, you also see that happen on mixing desks. At some points in the gain pot travel, the preamp switches stages (so basically goes to different sets of components). You often can hear an audible click from relays activating and a change in the SNR (I’ve experienced this many times using Yamaha digital desks and RIOs).
So this would be +0dB is dead in the middle of that particular gain range for this preamp…which kinda makes sense.

[Stinger22]

Using my P-90 equipped Sire H7V. Normal is input -3.7 then a gain block on each pre-set at +3.7. NR around 10%. That gets me just under the threshold bar on the input meter, even with a couple of boost and/or OD’s I have on a pedalboard before the QC input and then a good signal to the preset.

I turned off the NR and the turned up my input gain up and sure enough I hear the sudden dip at 9.3 but then comes right back. I don’t really hear much difference in the background noise. Setting the NR back to 10% gets rid of it. And around 12.3 I get the same momentary dip.