What Does a Compressor Actually Do to the Mix?

Compression is one of the hardest concepts to grasp. Even when you know that it turns the loud bits down, it takes further time and understanding to realise what potential that has on a track. A lot of compression technique just has to be learned the hard way, by doing the dirty work yourself. Anyway, I thought I'd do this quick post to demonstrate some of the applications of compression for those in need of help understanding.
ReaXcomp is a Free VST multiband compressor 

If you have no clue about compression at all, check here for a basic intro to the concept. Otherwise, here are the most basic of applications which cover the vast majority of compressor use.

  • Music will sound better when it is louder, if you A/B a track with one turned up, even by a dB, people will say it sounds better, even when not knowing why
  • Compression allows the track as a whole to be louder (just turning the track up may mean the highest parts clip) with a compressor turning down the highest volumes. It makes room for the volume to increase.
  • In terms of compressing a single sound, let's say vocals, its usually because you want the quiet bits louder. You know this technically. Combine this nugget of knowledge with the fact that vocals can get swamped by other instruments, you will realise by making the vocals a more uniform volume, you have to work less hard in the mixing to keep them on top.
  • If you are compressing a mix, let's say a grouping of the drums, you are doing it for the same control of volume but also power. New York Compression is a good thing if you have the time to read and try. The compression "beefs" up the mix sound and improves it (when done well).
  • Finally compression can be used in mastering to squeeze out as much volume as possible so the track can compare to others. Refer to loudness wars here. There are many applications beyond this but this was just a quick guide.