First off, if you have the luxury, don't compress going to tape until you understand compression better (then, I think its a perfectly fine thing to do). Rather, insert the compressor while you are mixing.
For now, don't worry about attack and release - set for fast attack, and medium release.
Gain Reduction (the heart of compression) is set with two controls: Threshold, and Ratio.
The threshold control determines what amplitude (volume) level, and above, the compressor will begin reducing gain. So, for example, setting the threshold at "-6" will make the compressor 'compress' levels of -6dB and above (and, -6 being a negative integer, by "above" I mean louder).
TV and radio stations always have a 'last chance' limiter set up right before the feed to the transmitter, to prevent distortion (the FCC basically mandates this), and they set the limiter right around -1dB, so that anything over -1 gets compressed down.
Ratio controls just how much reduction will happen to levels in excess of the threshold. For example, a ratio of 4:1 means for every 4dB over the threshold, only 1dB will come out of the compressor.
So, if our threshold is -3dB, and the ratio is 5:1, a signal with a level of +2 will come out of the compressor at -2dB. Check the math out: +2 exceeds a -3dB threshold by 5dB. Our ratio states that signals over the threshold will be compressed to allow only 1dB out for every 5dB in.
With the actual act of compression only capable of gain reduction (some people, myself included, could argue this point a little bit, I know), why is so much stuff which is 'loud' also 'compressed'?
Makeup Gain. Makeup gain (a common knob on compressors, sometimes labeled 'output') allows for the signal level to be boosted on its way out of the compressor.
When you combine makeup gain and gain reduction together, you get a less dynamic signal, and generally speaking, an overall louder, more controlled signal. Quiet sounds are louder, louder sounds are quieter. That type of signal is easy to mix, and its really easy to get it to 'ride' over top of your mix.
Attack, and Release control how fast the compressor 'compresses' when the threshold is exceeded, and how fast the compressor 'recovers' from a gain change, respectively. So if the compressor lowers the gain to reduce an incoming signal, and then the signal gets really quiet coming in, you might want to set the release appropriately so that the end envelop of the incoming sound isn't reduced because of a loud sound coming before it.
When you set your compressor up, start like this:
1) Put the attack and release controls at their fastest setting.
2) Decide on a ratio. Use 2:1 to 3:1 for a compression most people won't notice (but you, being the audio engineer, will). 4:1 is a good middle of the road setting, and 5:1 to 10:1 is pretty steep.
3) Set your meter (if your compressor has a meter), to show Gain Reduction (sometimes "GR" or "Peak Limiting").
4) Adjust your Threshold for a certain amount of gain reduction, based on what you are hearing, and what the GR meter says. If a signal only gets compressed now and then (GR meter moves now and then), you can prevent those occasional peaks and pops (such as microphone pops). About 3dB of gain reduction will get you some control over the signal. I've been told, and I've noticed it too, that reducing more than about 3dB will begin to get noticeable. Just keep that in mind - if you want a really compressed sounding vocal (like a radio talk show host), set the compressor so its always reducing - your GR meter is always showing gain reduction.
5) Adjust your Attack and Release for as natural - or unnatural - an envelop as you desire. Too long an attack might 'miss' a quick transient (like a snare drum). Too fast an attack may make the compression really obvious (you'll hear the compressor 'pull' the audio down). Sometimes, getting lots of GR, and then moving your attack so its fairly slow will create a nice controlled vocal sound.
6) Lastly, adjust your output, or makeup gain, so the signal is back up to the previous audible level (ie, not quiet).
You may also want to experiment with adding EQ before, and/or after the compressor - the placement of the EQ (before or after the compressor) will have a huge effect on the sound.
If I were trying for a hip hop vocal, I'd probably shoot for about 4:1 ratio, 6dB reduction, medium attack and release.
Or, you could try something a little less, like 3:1 ratio, and 4dB reduction.
For EQ, boost around 200-400Hz to add more 'body' - but be careful, you can make it sound like cardboard here too. Add around 4kHz-8kHz to boost presence. Try sweeping a third EQ around 300Hz to 1kHz for a really horrible sound, and then cut here (some people call this 'seek and destroy"). One rule I've heard and found to work well, is to boost with somewhat wide bandwidth ("Q"), and to cut with narrower bandwidth. I really despise rules like that though, so just play with it until it sounds good.
Here's to good tone
!
"If it sounds good, it is good". So in the end, screw all the rules, and just twist those knobs until it sounds good!
