Compression, what do those knobs do?
Updated: May 28
It's easy to look at a compressor and instantly feel a little overwhelmed, who wouldn't? There are a bunch of knobs and even if they are labeled it's not in an intuitive easy to understand way. My name is Spencer Miles. I own Spencer Studios one of the recording studios in Lancaster PA and today I am going to explain what each knob on your standard compressor does.
Today we are going to take a look at the dyn3 compressor which is a stock Protools plugin. Don't worry if you aren't a Protools user, these concepts extend to compressors in every DAW.
Dyn3 ( Dynamics III)
Before we dive into the specifics of how to use a compressor lets talk about the basics of what it does. In audio we can manipulate three things which are time, pitch, and volume. A compressor manipulates volume specifically by lowering it in a preset manner.
This compressor similar to the stock 7 band eq plugin we looked at in a recent article has input and output meters in addition to a gain reduction meter so we can tell how much our settings are lowering the overall gain. The gain reduction meter is useful as we can use it to approximate how much we want to adjust the gain knob upward after we have the compressor set. All the gain knob does is raise the volume and it is that simple.
Threshold or "thresh" establishes when the compressor comes on. Does it come on at a very loud dynamic or is it on when the volume is lower too?
The ratio shown in mathematical ratio form represents for every decibel over the threshold we are reducing (dividing) by x number. As an example 1:1 (1 to 1) means no reduction is taking place. 2 to 1 would mean for every x number of decibels over the threshold we are going to reduce it by twice the amount it exceeds the threshold by. Two to one is a very low ratio. Some compressors such as this one can compress all the way up to 100:1 even infinity to one. In this setting we would call it a limiter. A compressor is said to be able to function as a limiter if it can compress at 20:1 or more. A limiter is just a compressor with high ratio capability.
Knee works hand in hand with the threshold and determines the fineness of the threshold. Lets imagine the thresh is set at --22.0db . If we had a hard knee the line would be black and white meaning at -22.0 the compressor is on and at -21.98 the compressor is off. A soft knee starts to blur the lines a little bit allowing the compressor to more gently come on at lower thresholds before being in full swing at the set threshold. This can be used to make the use of a compressor less apparent.
Attack and release are more intuitive. Attack determines once the compressor is on how quickly are we going to intact the set ratio where release is the exact opposite.
The last item we have yet to cover is a side chain. A side chain is simple it is essentially an outside input that turns your compressor on and off. Let's say you have a side-chained compressor on your bass guitar controlled by your kick drum, when your kick makes a sound it will turn the compressor on and reduce the guitar volume using the set compressor settings.
A compressor is the strongest most versatile tool in an audio engineers arsenal. Understanding how to use it can make or break the project you are working on. If you'd like to know more feel free to reach out below.
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