What is compression?

What is compression?

Compression reduces the overall dynamic range of a

piece of audio by detecting when it exceeds a specified

level, and then attenuating it by a specified amount to sit all the same with the quieter level. Put

simply, it narrows the difference between the loudest and

softest parts of a track so that it’s more consistent in

level.

The parameters of a compressor

Though there are always exceptions, most compressors

share a common set of parameters. Understanding what

each one does will allow us to approach compression

with more Intentionality and ease.

Threshold

A compressor’s threshold, expressed in decibels (dB),

determines the level at which the compressor starts

compressing. The threshold can be set strategically to

target specific moments in your audio — for example, if a

drum groove’s snare is too loud, you can set the

threshold so that it’s low enough that the snare exceeds

it, but high enough that the rest of the kit is bypassed

(the best way to do this is slowly raise or lower the

threshold until the meter only reacts to the snare).

Attack and release

The attack of a compressor, typically measured in

milliseconds (ms), determines how quickly it pulls the

input signal down to the full ratio value when it exceeds

the threshold. The release is the opposite, representing

the total time it takes for the signal to return to an

uncompressed state.

Knee

The knee determines the character of the gain reduction

that’s applied to a signal. It ranges from a value of 0.0 to

1.0, with 0.0 being a hard knee and 1.0 being a soft

knee. A hard knee begins reducing gain abruptly when

the compressor exceeds the threshold, whereas a soft

knee introduces gain reduction gradually as the signal

approaches the threshold.

A compressor’s knee is more nuanced in its impact than

attack and release times, but can be valuable

nonetheless. In general, choose fast attack and release

times with a hard knee for more noticeable / aggressive

compression, and slow attack and release times with a

soft knee for subtle / gentle compression.

Make up gain

We often associate compression with making a track

louder. However, we’ve learned that by definition,

compression actually reduces level. Make up gain is what

allows compression to make a track louder. We can

compensate the level that we lost using this parameter,

and because we tamed the peaks, we can actually make 

the overall audio louder without running into clipping.