Shaw with some helpful advice on live audio:
A friend explained it to me like water. Gain is controlling how much water to let in, and Level is controlling how much water to let out.
Lower gain means less sound picked up overall (which helps with feedback) and the level will control how much you want coming out of the speakers.
You need to balance it a bit overall to get the right amount in the mix, but generally speaking go with as low of a gain as possible so you aren’t getting extra noise in the channel.
I ignorantly just thought of gain just as channel-specific volume. But it’s actually like increasing the sensitivity of the input. The mixer I have now has pretty clear controls for both, so being able to pull down gain and increase level should be great in any fight against feedback, and is likely to sound better if high-gain was letting in too much extraneous sound anyway.
I feel like most audio controls don’t have the separate controls though. I have an Elgato Wave XLR right in front of me, and it’s just one big knob. Is that gain or volume? It seems like that would be gain, and then you’d use software controls (e.g. Input Volume in my OS settings) for the volume, but actually as you move the knob the OS settings move to match. So I guess it’s gain? And volume only comes into play when the audio is being played back through audio output, or I’m in a Zoom call or whatever? But if I’m in a Zoom call, I don’t get a separate volume knob. So I just don’t see an opportunity to do a low-gain, high-volume situation in a typical digital audio situation.