Here’s Your Beginners Guide to Audio Compression

Jordan Tracy’s simple explanation of compression will help your sound team:

[Editor’s note: I often have trouble hearing a consistent, strong lead vocal mix in smaller churches – compression fixes this!]

There are fewer tools more mysterious and complicated to an audio engineer than a compressor. A lot of inexperienced engineers can apply a compressor with the wrong settings and end up making everything sound worse. One thing is for sure, if you don’t understand how a compressor works, you can never master the use of one. Before I start I’d like to say that no two audio engineers agree 100% on the proper use of a compressor. It’s my hope that in giving you the definitions and functions of each part of the compressor, it will help you come to your own formulation of how you would like to deploy one.

Purpose
A compressor applies an automatic gain reduction to a signal, with a given ratio above a set threshold. You use a compressor to control a channel that has a high dynamic range to smooth it out. This is an essential tool when mixing vocals or even spoken word. When you get a vocalist or pastor that has a large dynamic range, you can use a compressor to help you not need to ride their fader as much as their voice changes dynamics. Compressors can also be used to smooth out instruments as well as an entire mix. The possibilities are endless on how you can use a compressor.

Threshold
The threshold is the first and arguably the most important setting on a compressor. It is the spot that you set for when the compressor will kick in. Your compressor will not do anything until the signal reaches that threshold.

Ratio
The Ratio is the amount that the unit will compress or reduce the signal after it passed the threshold. Ratios are measured as 2:1, 3:1, 5:1, 10:1, and anywhere in between. The 1 in the ratio is the signal that is unchanged, and the first number in front of it determines how much will be reduced. So if the ratio is 2:1, the signal will be reduced by 2, if the ratio is 5:1, the signal will be reduced by 5, and so on.

Knee
The function of the knee, is to tell the compressor how to transition from the unchanged signal to the compressed signal once it has passed the threshold. A soft knee is a smooth and gradual transition from uncompressed to compressed. A hard knee is a more noticeable switch from uncompressed to compressed. Generally speaking a softer knee would be great for spoken word or vocalists, and a hard knee is used for kick drum or bass.

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