Music Production Essentials: Compression Controls

Compression can work wonders to boost the energy of an audio track, but if you’re new to using the effect it can be difficult to hear and to understand exactly what’s going on. Here’s a comprehensive explanation of the controls on a standard compressor used to shape the effect and generate the sound you’re looking for.

Threshold and Ratio

The threshold and ratio values of your compressor work together to determine the level of the effect – whether your signal will be very compressed, or barely compressed at all.

First, a threshold is set to indicate a volume level so that anything louder than that level will trigger the compression effect, reducing the signal’s volume.

This massively important control will determine how much of your track will have compression applied. Often the threshold is set so that only the peaks are compressed, whereas a very low threshold could compress the whole track, and a threshold that’s too high won’t compress anything at all.

The compressor ratio sets how much the signal is reduced when it goes above the threshold. For instance, suppose at a certain point a track is 12 DB louder than the set threshold. If the compression ratio is 2:1, the compressor would reduce the signal by 6 and allow 6dB of signal above the threshold. For every two DB above the threshold, one DB of that signal is allowed to sound. If the compression ratio is 3:1, the compressor would reduce the signal by 8dB and allow 4dB of signal above the threshold – for every three DB above the threshold, one DB of that signal is allowed to sound.

Anything over a 50:1 ratio is no longer considered a compressor, but instead, a limiter. As the first number increases, this is considered a higher compression ratio, and an infinite compression ratio would not allow any sound above the threshold whatsoever, creating a “brick wall limiter”.

Essentially, the lower the ratio, the more dynamics are allowed to sound.

Attack and Release

The attack parameter on a compressor determines how quickly the gain reduction is applied to signal above the threshold, and the release parameter determines how quickly the gain reduction is backed off.

With a long attack, The compressor will be slower to apply to gain reduction to the signal, and allow the initial hit, or transient, to cut through. With a zero attack value, the compression will be applied immediately.

With a long release, the gain reduction will be applied for a longer period of time. With a short release value, the gain reduction effect will go away more quickly, allowing the audio level to rise back up if the release is short enough relative to the transient signal.

Not sure where to put compression in your signal path? Check out our guide to optimizing effects order!