It depends on what you want to use it for. Generally compressors are inserted in any of three places: on the
channel, on the subgroups, right before the amps. Don't take that as gospel.
The
channel: you use the
channel's insert
jack to run out to the
compressor and back. Generally for
theatre, I avoid compressing individual singer's channels. However, I do put a
bit of compression on things like
bass, drums, and acoustic guitar. You'll need an
insert cable for this, which is a 1/4"
TRS jack going to two 1/4" TS jakes. I believe most
console have the tip as
send on the
TRS plug and ring as the
return. You can make your own, or Banjo Hut has them for around $10 last time I looked.
The subgroup: I'm not sure the cheaper boards have inserts on the subs, but if they do, you can use this technique. On one run I was on, the male leads were sent to subgroup one, female leads to sub 2, male chorus to sub 3, female chorus to sub 4,
etc. We had Focusrite Red 3 compressors inserted on the lead channels, and dbx 160's inserted on the chorus, just to tame them a little
bit for the
system. Keep in mind that if you do it this way, the loudest singer/
instrument/whatever will in essence determine the overall
level. It's the one that'll trigger the
compressor, which will bring everything down in addition to the loudest thing. This problem doesn't exist if you compress on an individual
channel basis.
Before the amps: If I have an analog driverack, I like compressors right before the
crossover. In this case, they act more as limiters than compressors, protecting the
system from
clipping. Most
DSP units have limiters built-in to the individual outputs that you can control, so the highs go into limiting before the lows, to take an example. If you go this method, you simply hook it up in-line between your EQ and
crossover (or amps if you're running full range). You'll need one
channel of compression for each driveline if you want to compress all of your outputs, or you can just use two and limit the L-R sends. A note of caution with
system limiters: if you keep running the
system hard and into heavy limiting for an extended period of time, the overall
power going to the speakers increases, and in most cases will burn up the
voice coil.
One other trick that I've learned since working, but haven't tried yet. If you have really long drive lines to your amps, you can put a
compressor inline with the board's output. Set it so that it's not compressing anything, but you can dial up makeup
gain, creating a sort of
line driver to drive your amps. Again, I've never tried it; it's just hear-say.
Finally, with compression, a general rule of thumb is that if you can hear the
compressor doing its job, you have too much compression going on. I suggest that if you (or your sound guy) have never used compressors before, hook it up on your CD
channel and experiment with it for a little while to see how it affects the sound.