Threshold

This is the level at which the compressor kicks into effect.

A high threshold means less compression and a low threshold means more compression as more of your instrument’s signal will be crossing the line and making your compressor start the attack phase.

Ratio

This controls how strong the compression effect is.

A ratio of 2:1 is normally the lightest option. At 2:1 your audio – once past the threshold level – will get 1dB louder for every 2dB louder the input to your compressor gets.

Generally, if you get to the level of 20:1 and above that’s regarded as limiting rather than compression.

Attack

The attack control is a speed control.

What you’re setting is how long it takes for the compression to take effect after the threshold has been crossed. This is really useful for adding punch to your sound – allowing that small amount of louder, uncompressed signal to get through before the compressor grabs and controls the sound is where a compressor can really help your track to kick.

You have to adjust to taste – too quick and not enough of your sound will come through to have a noticeable effect, and too slow means that your sound will have dropped below the threshold level again before the attack phase starts, so no compression.

Release

This is a speed control too.

Here you are deciding how long it takes for the compression to ease off once the signal has gone back below the threshold again. Faster makes the compression more obvious (remember this is not a bad thing!) and slower can end up making the sound less punchy.

Again, it’s best to adjust by ear – and be careful not to go too fast as that can produce some ugly ‘pumping’ effects. Unless that’s what you’re going for, in which case get stuck in!

My rule of thumb is to adjust the release knob so that it is releasing in time with the music. That way the dynamics of the track are moving with the beat and the whole mix is feeling more coherent.

Knee

This effect is slightly harder to hear (so not one to worry about too much if you are new to this game).

You generally have a ‘hard’ or ‘soft’ option here, but occasionally you get a knob instead so you can set it however you like. What you’re setting here is how abruptly the compressor kicks in once the attack phase is over.

With a ‘hard’ setting your 2:1 / 4:1 / whatever compression is effective the moment the attack phase is over. With a ‘soft’ setting the compression comes in a slightly gentler way. The soft setting is useful if you want to use higher compression ratios but not get too punchy about it. Hard settings can add to the punch that you’re dialling in.

Make-Up Gain

This is fairly simple. As you compress the louder parts of your signal you are naturally turning down the overall volume of your sound. You can turn it back up again using this ‘make-up gain’ control.

It’s at the end of the chain so doesn’t affect how the compressor reacts, it’s just for matching the output level to what it was before it was compressed.

This is useful for hearing exactly what the compressor is doing. Once you’ve adjusted the make-up gain so that it sounds the same overall level before and after the compression is applied then you’ve got a clearer picture of the effect that the compressor is having.

Match levels, hit bypass on and off, see if you prefer it compressed or not, adjust to taste.