Audio Compression Explained: A beginner’s guide to understanding compression

Audio Compression Explained: What is an audio compressor?

A compressor is a plugin or a piece of hardware that reduces the dynamic range of an audio signal. In most applications, it does this by turning down the loud parts of a signal.

Why use compression?

Well, there’s nothing wrong with music having a strong dynamic range. In fact, dynamic range can be one of the things that makes music interesting to listen to. But on a practical level, large changes in dynamics can cause a problem. Imagine a scenario where a singer performs some parts of a song loudly and other parts quietly. Where do you set the fader? If you set it to the right level during loud parts, then the level will be too quiet when the singer performs quietly. But if you set it to the correct level for the quiet parts, the level will be too loud when the singer performs loudly.

The answer is to use compression to reduce the difference between the loud parts and the quiet parts. A compressor reduces this difference by turning the loud parts down for you. You could of course automate the level of the fader to turn the level up or down according to how loud the singer is performing, but with a large track count, and with most tracks having varied dynamics, that’s a lot of automation to carry out. So a compressor does this job for you.

But that’s not where the use of a compressor stops. Due to the huge amount of control you have over the way a compressor turns down specific parts of a signal, you can use it to really sculpt sounds. For example, you can use a compressor to make an instrument sound more punchy. You do this by having the compressor apply gain reduction to the decay portion of the instrument’s notes, in turn emphasizing its attack. Or, you can use a compressor to make an instrument sound fatter or fuller. You do this by having the compressor apply gain reduction to the note’s attack, in turn emphasizing its decay. Either can be achieved simply by having the compressor turn down specific parts of your audio signal.

Audio Compression Explained: How do you use a compressor?

A compressor offers you a large amount of control over how dynamic range reduction is applied. When you use a compressor, you decide what level the compression kicks in at using the threshold parameter. That means you can let everything below a certain level remain uncompressed, and have the compressor apply gain reduction only to parts of the signal that go above that level. You can also tell the compressor how much compression to apply once the signal breaches that threshold level. This is done using the ratio parameter. So you could have the compressor turn the signal down a lot or just a little.

You also control how quickly the compressor applies the gain reduction using the attack parameter, and how quickly gain reduction subsides using the release parameter. These parameters let you take control over the way that compression is applied to a signal, and make-up gain, hold, look ahead, and knee parameters offer further control still.

Audio Compression Explained: Conclusion:

So, that’s audio compression explained. You can apply compression to any audio signal and have it turn down specific parts of that signal in exactly the way you want. This gives you the ability to alter the dynamic range of a signal to achieve multiple different results.

Do you use compression in your mixes? If so, what do you use it for? Leave your thoughts and questions in the comments box below.