gain vs. volume fader

[MikeRivers]

 

The trim pot -- this essentially controls the gain of the preamp stage. You want this high enough to get above the preamp's noise floor and low enough so that you don't overload it or the next stage.

You definitely don't want to overload the preamp stage. That's part of setting the gain correctly. But any competently designed mixer won't overload the next stage before the preamp overloads. That would be a very bad design.

So you will always shoot for a "just-right" level, here.

That would be true if what went in never varied in level. You can't go chasing the input source with the gain control all night. This is why you want to set it so that you have some headroom for unexpected peaks. Knowing how much lower to set it than at the clipping point when what you are told is the loudest the input will ever be is a skill, and to a certain extent, luck. In the studio, you typically leave plenty of headroom because you can hear if things are too noisy and do something about it, and you don't want any distortion. Live sound engineers often run the mic preamp gain very close to clipping because they want all the level they can get out of the sound system (it's their job to make it LOUD).

 

Nobody's going to notice a little distortion on the kick drum, in fact, it might even enhance the sound. But the problem here is that there may not be enough headroom on the mix bus when you have all the channels cranking at near maximum input to the faders, and the faders keep creeping up during the show.

 

As a benchmark, in Mackie's manuals, they explain a procedure for setting the preamp gain using the Solo button on the mixer. They tell you to solo the channel (the meters then read the preamp output) and adjust the trim so the meters read 0 VU with a "normal" input. This leaves about 20 dB of headroom, which is sufficient for a fairly full mix with the faders at their "unity" position without overdriving the bus. But if you set the gain so that all the channels are just below clipping at the preamp, you'll find that the mixer doesn't have enough internal headroom and what goes into the master fader will clip.

[Rudolf von Hagenwil]

 

Pardon my ignorance, but I thought that you should set the input gains by using the PFL button on each channel to get the hottest signal before distorting, then using the faders to set the levels.

 

 

I am afraid that when every signal of every channel is as hot as possible, it will add up to overload and distortion. A better advise would be to set the input amp (gain or trim) at what each incoming signal needs

[blue2blue]

You definitely don't want to ...

 

Thanks for the valuable elaboration, Mike! It's one thing to know the functional theory and it's another to have practical strategies for real world situations.

 

As you may know, I have a tendency to overelaborate, and I was fighting that.