Compression Explained

What do all those setting on a compressor do?

First off I want to say compression was something it took me ages to understand. I just played with the options till it sounded how I wanted. Ultimatley it took me a while to realize what each option did. I will try to explain how it works and describe what the standard control parameters do.

There’s a few concepts and resulting controls on compressors.

Threshold
Ratio
Attack
Release
Knee
Gain (makeup gain, output, auto)

Threshold:

When the audio exceeds a defined level the compressor kicks in and starts “compressing”

Ratio:

The amount of compression. Once the threshold level is reach and the compressor starts compressing the ratio defines how much compression will occur. The ratio numbers refers to how much each db over the threshold will be compressed or how many db’s over the threshold (first number) it will take for the output to inclrease (second number). For example a 4:1 (four to one) ratio means that it will take 4 dbs of audio over the threshold before the output would increase by one db.

Attack:

How fast the compressor kicks in once the threshold is reached.

Release:

How fast / slow the compressor stops compressing once the audio goes below threshold.

Knee:

How hard or soft the compressor starts to react. A soft knee is like an arch, hard knee is more like a defined angle. Soft knee acts on the attack and ratio and threshold in that the compression starts at a lower threshold and increases slowly/smoothly as the threshold is reached. . . it softens the response of the attack and threshold creating a less noticeable compressed sound since it slowly starts to compress sooner and eases into it.

Gain / Makeup Gain / Auto makeup:

Once the signals output has been reduced by the compressor settings the level would be lower and therefore most compressors have a Gain / Output / Makeup Gain / Auto makeup control. This just turns up the output of the compressed signal. Auto make up simply does this automatically so as the threshold/ratio is adjusted the output remains the same.

Heres some additional info:

http://en.wikipedia.org/wiki/Dynamic_range_compression#Soft_and_hard_knees

• 
• 
•