The gain controls the level out of the preamp.

On most boards, the GAIN is, essentially the "sensitivity"of the INPUT stage of the channel. The fader sets the OUTPUT of the channel feeding the various buses subsequent to the input preamp.
The reason there are (2) "volume" controls (your friend's terminology, not mine!) is so that you may "match" the level of the source to the "nominal" operating level of the preamp circuitry it's "hitting". For example: You stick an SM-57 into the front of a roaring Marshall amp.
That 90dB+ sound pressure level is going to generate a very strong output voltage from the mic to your channel input. Now that channel input has to be flexible enough to handle not only that signal, but, say the female back-up singer (say, 10-15dB quieter) on a 58. The GAIN control lets you adjust the amp mic DOWN to prevent overloading the preamp (which would cause massive distortion), and adjust the singers' channel UP to get the signal over the residual noise level of the preamp. That's why they have those little red LEDs on the channel-to let you know the signal needs to be turned down at the preamp gain. If you have an additionl green LED, it's usually used to let you know when to turn that Gain control UP.
Once you have that Gain control set at the proper level, you use the fader to MIX the channels, and that position of it should be somewhere approx 2/3 up on its travel, but that depends on the design of the board. Basically, if you are getting enough signal in the mix while the fader is barely "up", you are probably running the Gain control too "hot". and vice-versa: if you are pushing the fader to the max, you are setting the others incorrectly. This is what is referred to as "gain staging"and is mandatory to learn to correctly operate an audio mixer. Capiche?

Tell him that the gain is the water main for a house. The fader is your water faucet's. Simple.

Great analogy, Sheet! Does that mean that the comode is the monitor send? ( I know of a couple of IEMs I'd like to flush...)

Gain is like the water main

Sheet -> I have been thinking about your water main analagy and as there are many gain controls for each channel on a mixer whereas there is generally only 1 water main for a property, I would probably describe the water main as the two main left+right faders that control the output from the mixer if you were looking at it from the output in?

Good points.

Other thing is that it gives you better control. You adjust the gain to give you optimal thru put when the fader is in position Unity gain.
When that's done you have full control. you know that if the fader is at Unity gain its as high as it goes before peak.
Without a proper gain adjustment the fader handling would be messy.
The signal would maybe only fit in a small specter of the fader.

It's hard for me to put it to words in English :D

Explaining....

This is precisely the problem I have too! :?

I know how they both work but you just can't explain it easily in plain English!

As you say HansAM - You set the fader to unity (0dB) and then the gain is adjusted so that the level is just below peak.

That works on some makes of boards, but certainly not all. Some boards don't have "unity" until the faders are maxed out. Others the faders are a real gain stage early in their travel. On many mixers, the EQ will have a say in where the Gain control at the front end is set. Realistically, the fader position shouldn't dictate how the Gain control is set. The source does that.

moonbaby wrote: the fader position shouldn't dictate how the Gain control is set. The source does that.

Everything is relative. You might have to adjust gain as you go along. Utopi is to have everything at Unity.
This also depends on what sounds best on your board. Maybe you wanna put the fader in Unity and adjust the volum with gain.. Just cause it sounds better.

And absolutly MOST pro mixers have a Unity gain level on the fader, and then some more.

And EQ'ing should be (utopi) at a minimum. You usualy take some off. Boosing the EQ is in most cases just covering the problem.

All very good and correct points, To add to it though:

EQ's generally work better when they are fed with a good signal, If you find you are boosting/cutting a lot, with not a lot of change it tends to indicate that your input gain is on the low side.

Another thing to note is that all your Aux sends have the appropriate signal to play with...

As a general rule, the gain is there to boost/cut the amount of signal coming in up or down to the right level for everything down the chain from it to work at it's best.
(best SNR, no distortion, any inserted equipment having appropriate levels,EQ working effectively, auxes and bus out faders/pots all with useable travel in them)

it does vary a bit where it tends to work best, but the general rule stays the same..

I really gotta work on saying what I have to say with less words.........

Al 8-)