The way a sound board works is that it gets an input. That input goes through a series of modifications, or can be left clean. If modified, it can be modified on the channel (the specific input and that input only), or it can be lumped together with all the rest of the inputs and all of them modified the same. Then it gets output two ways. One output is to a series of monitors. The other output is to the speakers that make noise in the house.
Monitor outputs are usually either to an in-ear monitor, or to a small box on the stage. In either case, they are meant for one person to hear. The little boxes on stage are highly directional in how they produce sound. Big dang speakers that thump whole rooms are direct sound widely. This is the biggest difference between a monitor and a speaker.
Sound is mixed differently into every monitor. The lead guitar player has a completely different mix in his/her monitor than the drummer or the bass player or the vocalist. For example, when I was in a band, the rhythm guitarist was also our lead vocalist. She did not like to hear bass in her monitor. She wanted to set the rhythm, not react to it. As the bassist, and knowing that she wanted to set the rhythm, I had to have her guitar in my mix loudly, and I also had the vocals and lead guitar so that I could hear them. The drummer didn't have anyone in his mix and just banged on the drums. The lead guitarist had the bass so loud that I often got in trouble for having my on-stage amp up too loud.
So, each member of the band had a different mix that they were listening to, and then the floor speakers had a completely different mix. Often sound board guys will wear headphones so that they can only hear the mix that's going to the floor speakers instead of the floor speakers themselves (which has a little bit different sound depending on the acoustics of the venue).
So, now you've got that.
How do you get the signal from your mouth or your fingers to the board so that the board tech can do all this tweaking, mixing, and distributing to various boxes both big and little?
That's done with cords. It can be done cordlessly, but then radio signals take the place of cords. So let's just pretend everything has cords. You sing into a mic. The mic converts your voice to analog signals. Those analog signals travel down the mic cord to a flat box with a bunch of numbered plugs on the floor of the stage. That flat box is attached to a bunch of cables that run to the sound board and ends at a series of numbered jacks. That flat box and the cable all the way to the box is called a snake. Let's say your mic is plugged into jack 1 on the snake. At the sound board end, there's an XLR jack with the number 1 on it. That goes into channel 1 on the board. Then the sound guy can modify that analog input from your mic by pushing it left or right in the floor mix, or boost the low end, or cut back the high treble range, or put a little reverb on it, or make you sound like a robot, or whatnot. Take the simple case of plugging your guitar into the snake instead of a pre-amp or amp. It goes the same way into channel 2. Now lets keep it simple and say that you're playing with just a bass player who doesn't sing, and so there's just one more instrument plugged into the snake on channel 3.
At this point, you would not be able to hear the bassist at all. The floor speakers are designed to make sound go out to the floor, not to sound good on the stage. So if you're singing and playing, you need to know what the bassist is doing and vice versa. That's where the monitors come in. You will each have a monitor on stage pointed at you or in your ear. Box monitors are easier to describe, so I'm going to go with that. The sound guy will listen to your directions and mix your voice on channel 1 up pretty high so you can adjust on the fly, your guitar on channel 2 for whatever reason you want to hear your guitar in the mix when you'll kind of a little bit be able to hear it acoustically, and the bass kind of loud because that is the only way you're going to hear it on channel 3 so that it sounds a way that you need to hear it to keep track of how it all sounds. That will be output to your monitor, which is highly directional and pointed straight at you. The bassist will probably want to hear what rhythm you're playing on the guitar the loudest, what he's doing on bass mixed under that, and your voice probably pretty low in the mix unless he's going to need verbal cues. So you're each going to experience the sound of that concert completely differently, and neither of you are going to hear it the way you'd want to if you were in the audience. The sound board guy is going to put that mix to something that sounds good and you will not have any way of knowing what that is until you hear the playback tapes (and even then maybe not because they can usually have yet another mix).
Let's start to complicate it. You can put your mic and guitar to a pre-amp that will allow you to modify and mix the signal that goes to the snake. You'll usually have only one output on the pre-amp to the snake (though there are multi-channel pre-amps).
We can complicate even more. Let's pretend that you're Brian Seltzer. He likes to play his guitars clean and use different amps to get different sounds. So he's going to have a bunch of amps on the stage, and a bunch of guitars on the stage. To get those clean signals to the snake, the best way to do that is to mic the guitar amp. But if you make changes to the tone or volume settings on the guitar or on the amp, those are going to go right to the mic. A lot of guitarists who like a tube amp sound take this approach. It's very common to see a practice size amp on stage with a mic in front of it. This is the reason. The guitarist wants the particular sound of that amp, and woe be unto the sound man who alters the channel in the mix.
In ear monitors add another level of complexities because they often have a means to remix the signal from the board for the individual listener.
Whenever something in all of this goes wrong, all sound techs begin to check wire connections, which they do for 45 minutes before they realize that they forgot to push the button. Then they unplug a cord, plug it back in, say "that ought to do it", create a sound disturbance to make everyone look away from the sound board, then they push the button when no one is looking. It is never the cord. It is always the button. The cord will always be blamed.
- Zurf
Granted B chord amnesty by King of the Mutants (Long live the king).
If it comes from the heart and you add a few beers... it'll be awesome! - Mekidsmom
When in doubt ... hats. - B.G. Dude
