Compression – Part 1 – Here’s The Basics.

Learn how and why a professional mix engineer uses compressors.

Dom Morley
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24th April 2020

Welcome to Part 1 of our series on compression.

Here I’m going to give you the low down on why we use compressors. Including my (semi-controversial) ideas on when we shouldn’t use them.

Gain Reduction

Compressors have two jobs.

Firstly, they reduce the volume of loud sounds and increase the volume of quiet sounds. This levelling-out process is why compressors where originally built in the 1930’s – back when they only had ‘in’ and ‘out’ sockets with no controls.

They were used by broadcasters to control the volume changes between (for example) a presenter talking and an audience responding with applause.

These boxes became popular because they had faster response times than a person holding a volume knob trying to do the same job. All very sensible.

The Envelope

However, the opportunity to be less sensible came when manufacturers began putting controls on the compressors, with control over compression ratio, attack time, release time and so on.

With this development compressors could be used to actually shape the sound and not just level it out. Which is their second (and considerably more interesting) function.

Moving Forward

Scroll forward a few decades, and what strikes me as odd is that many people are still using compressors for both of these jobs.

While they remain an excellent tool for shaping and changing the dynamics of the sound, DAWs left them behind years ago as the best tool for levelling out volume. If you need to adjust volume changes in your mix then get stuck into the automation and you have absolute control over every aspect that you could wish for.

Compared to volume automation, compression is an extremely blunt – even primitive – tool for controlling level.

Anyway, I got a bit rant-y there. Sorry about that! Hopefully you get the idea though.

Check out the other parts of this series:

Compression – Part 1 – Here’s The Basics
Compression – Part 2 – Controls
Compression – Part 3 – Alternative Uses
Compression – Part 4 – Styles Of Compressor
Compression – Part 5 – Getting Personal