Compression is one of the most important tools for recording and mixing music. A compressor is used to control the dynamics — the variation between the softest and loudest parts of an audio signal. Dynamics can add life and a sense of movement and drama, but dynamics control is vital in making a track sit properly in a mix — as long as you’re careful not to use too much.
Some engineers like to record through a hardware compressor. This is a great way to keep the recorded track at a consistent level for a more even recording. But when compressing while recording material, be sure not to squash the signal too much. Too much compression on input will leave you with a flat, lifeless track. And if you killed all the dynamics while tracking, there’s no way to get them back.
The same basic rules apply for compressing a track while mixing, whether in the studio or on stage. Use compression to make sure that the softest parts of a track or channel don’t get lost in a mix, and that the loudest parts don’t overwhelm the mix.