2. Compressors

Compressors work similarly to gates, but it can be a lot harder to hear what they're doing.

(If you ever come across a "leveling amplifier" its a compressor that thinks it's hot shit.)

Usually they'll have a threshold level, attack, hold, & release, that are pretty much the same as in a gate. Anything below the threshold level is not affected. Attack is how long for the effect to turn on completely once the threshold is breached. Hold is how long it stays completely on. Release is how long it takes to go back to normal. (Assuming the threshold is not hit again.)

The other big controls are Ratio and Output Gain/Makeup Gain/Gain. The Ratio is always presented in this form (1:1, 2:1, 3:1...). What a 2:1 ratio means, is that for every 2dB a sound goes above the threshold, it comes out only sounding 1dB louder. So if I had a threshold of -10dB and a ratio of 2:1, and sent a 0dB sound through my compressor, the sound would come out -5dB. This is because it was 10dB over the threshold, and only went up 1dB for every 2 it would have uncompressed.

Choosing the right ratio is very important. It determines how much compression there is. The higher the ratio, the narrower the dynamic range of the signal becomes. Compressors with a ratio of 8:1 or more are sometimes called Limiters or Limiting Amplifiers. Higher ratios are sometimes necessary when recording inexperienced performers who don't have much control over their instrument. It can make them sound a lot tighter. What you're essentially doing is leveling out the volume of the track. This makes it easier to keep an instrument in one place in the mix. An instrument with a real high ratio stays in one specific spot. An instrument with a 2:1 ratio has a decent amount of room for movement. (1:1 means the compressor isn't doing anything.)

Most compressors will also have a display of the gain reduction occurring. That means how much quieter the output is than the input. This will tell you how high to set your output gain. Once you have the compressor set how you want, bypass and un-bypass it until the volume sounds about even both ways. You want to make sure the compressor doesn't just sound better cause it's a little louder. You can use compressors for extra gain if you have a quiet signal, but when you can use your faders for that.

Some compressors may have an Input Gain control which is replacement for the threshold. In that case the threshold is fixed, and the input gain is boosted to push more of the signal over the threshold. (You can use compressors like that just to add their tone to a signal without really compressing it. Leave the ratio at 1:1 and boost the input gain. By the same amount you reduce the output gain. It sounds good on real tube compressors, might not sound as good on lesser plug-ins.)