What is Compression?
Also called: dynamic range compression, compressor
Compression is the process of automatically turning down the parts of a signal that go above a set threshold, which reduces the difference between loud and quiet moments. It is used to control, glue and shape sounds in a mix.
A compressor has a few main controls. The threshold sets where it starts working. The ratio sets how strongly it reduces the level above that point. Attack and release set how quickly it reacts and lets go, and makeup gain brings the overall level back up afterwards.
Different settings have very different effects. A slow attack lets the start of a drum hit through before the compressor clamps down, which adds punch. A fast attack catches peaks and smooths a vocal. Gentle compression on a group of instruments, often called bus compression, can make them feel more like one performance.
Data compression, the kind that makes MP3 files smaller, is a different thing that only shares the name.
Example
With a 4:1 ratio, a vocal peak that goes 8 dB over the threshold comes out only 2 dB over it.
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