What is a compressor?
A compressor is a dynamics effect that automatically holds down sounds above a level you set. It evens out the difference between the loud and quiet parts of a performance, making a vocal easier to hear, stabilizing the level of a bass, or changing the attack and the density of drums.
The main parameters
Threshold is the level at which compression starts, and Ratio decides by how much sound above that level is held down. Attack is how quickly the compression takes effect, and Release is how quickly it returns. Makeup Gain compensates for the level lost to compression. The Gain Reduction meter shows how many dB are being held down.
More than evening out levels
A slower Attack tends to preserve the attack of a sound, while a faster one holds peaks down more. The length of the Release changes how the level moves and how the rhythm feels. So even when you even out the same level differences, the settings change how it sounds.
Do not overdo it
Compressing deeply all the time can flatten the dynamics of a performance, make it sound choked, or produce the unnatural level movement known as pumping. Rather than aiming only to make things louder, match the levels before and after processing and compare the differences in tone and movement.
Different designs sound different
Compressors come in types such as VCA, FET, and Opto, which behave and sound differently. Some hold peaks down fast and precisely, others move gently and musically. At first, rather than memorizing the type names, switch between them on the same sound and listen to the change.
Using a sidechain
Driving the compression from another track used as the detection signal is called sidechaining. It is used for ducking, where a bass or a synth is lowered only at the moment the kick sounds. For concrete settings, see How to create ducking in EDM (Japanese).
