MIxing Tools: Compression

Compression is one of the more vague mixing tools, yet the one that few mixes can use without. A compressor is a dynamic prosessor. This means that it processes the dynamic range of a signal. In music dynamics is defined as the difference between the loudest and the quietest parts of the song. A compressor does what the name suggests, and compresses the dynamic range of a signal.

A compressor is actually an automatic gain rider, doing the job that sound engineers had to do with fader riding in the studio/stage/broadcasting studio so as to have a good overall level without letting the peaks overdrive the tape machine/cirquitry and recently AD converters. A compressor takes on this job by reducing the gain of a signal whenever the signal passes a threshold level. This means that all the dynamics over the threshold are reduced, therefore reducing the dynamics of the overall track, enabling the engineer to have a louder average signal without clipping (overdriving the cirquitry).


Well, thats cool I guess. So how does a compressor work? A compressor is one of the most useful tools in mixing when used correctly, and as all tools, can be destructive if used incorrectly. To the right there is a basic software compressor. The controls are the ratio, threshold, attack and release. The ration determines the rate of gain reduction. On the graphical representation the ration determines the slope of the upper half of the curve. A ratio of 1:1 will rueslt in no change while 1:1000 (or infinity) will result in a horizontal curve. The threshold control determines the level at which the gain reduction kicks in. Graphically the threshold is represented as the "break" in the curve. The attack and release controls are the most important controls to understand, as they determine how fast the compressor reacts and when the gain reduction ceases after the signal goes below the threshold again.

In Use
A compressor is most commonly used to create a balance in a mix without having to automate to much. It can "tighten" up a performance that is uneven because it brings the peaks closer to the "valleys." Getting a controlled vocal track for instance, where there is alot of dynamics, you can pull up the quiter sections without having the loud sections become overpowering.

For percussive instruments a compressor can be very useful. By playing around with the attack and release settings on a compressor you can let the initial attack of the snare (f.eks) pass through, while the gain reduction kicks in and dampens the ring of the drum. This method also works the other way round, by having a short attack time and a short release time the attack of the snare will be attenuated while the ring will be left unaffected. Compressors are good as transient shapers, and if used properly can really help a track become punchy, in your face, or pull it back and move it away from the focus point.

PLay around with them, more info will follow. Meanwhile you can send me a mail to robin.bjerke@gmail.com or post a comment if you have any questions.

Peace