I get it. Compression can be incredibly intimidating. Nevertheless, it is absolutely imperative that you understand how to use a compressor. Compressors are usually used on almost every track in a mix session. Every compressor does the same thing in different ways, so once you learn one, you’ve learned them all. I’ll walk you through the basics of some of the settings that you will come across using various compressors.
The shortest answer is that a compressor reduces the dynamic range of a signal. This means lowering the highest parts and raising the lowest parts so that everything is at a more consistent level. For example. a vocal take typically has some very loud parts and some very quiet parts. Adding a compressor would make a more even sounding vocal take.
Threshold – This is the loudness point at which the compressor will begin to start affecting the signal. A higher threshold will have a lighter effect while a lower threshold will have a heavier effect. This is usually measured in dB (decibels). For example, a compressor with a threshold of -20dB will not do anything until a signal louder than -20dB plays.
Ratio – The ratio represents how much the signal will be affected once it hits the threshold described before. This is represented by 1:(n). Most compressors will be set between 1:3 and 1:10, but also go much higher (literally all the way to infinity, but dont worry about that for now). What does this mean though, you ask? Well with a 1:3 ratio for example. for a signal hitting our threshold, for every 1 dB above the threshold, the compressor will reduce the output by 3dB. 1 dB : 3 dB.
Attack – Once a signal has crossed the compressor’s threshold, how long will it take for the signal reduction to take effect? This is represented in milliseconds (ms). For example, a compressor with an attack set to 1ms would allow a (basically) indescernible amount of signal through before it reduces the signal. while an attack of 15 or 20 ms would allow 15 or 20 ms of unprocessed signal to bypass the compressor before it would take effect.
Release – This is basically the opposite of attack. Release is the amount of time after the compressor kicks in that it takes for the compressor to stop reducing the signal. This is also measured in ms. A release set to 10ms would stop compressing the signal almost immediately after falling below the threshold while a release time of 1500ms or more would effect the signal for quite some time after the original signal crossed the threshold, which can have a very desirable effect.
Gain – After applying a compressor to a signal, the overall loudness of the signal generally is going to have been reduced. This post-gain is used to compensate for this and add loudness to the post-compressor signal. This is usually measured in dB.
There are more settings than this on some compressors, such a knee, Dry/Wet, and Key Input, but these are more advanced settings (which you should still learn about) which are not quite as essential to understand. Hopefully this clears up some of your confusion regarding what all those knobs mean on your compressor.
Now that you understand the anatomy of a compressor, its time to learn how and when to use one! Stay tuned for a coming post about Compressor Technique!