This article covers compressors and how they are utilized to control the dynamic range of an instrument or vocal. Compression is a process that reduces the volume of the loud portions of an audio signal and amplifies the quiet portions, effectively narrowing or compressing the signal’s dynamic range. Compressors can also be used as limiters to set a ceiling on the dynamic range, causing everything above that ceiling to be lowered to a recordable gain level. This is done in order to combat clipping/distortion in the signal. When working with compression, there are several settings you need to take into consideration in order to control the level of the signal properly. Among these are the Threshold, Ratio, Attack, Release, Input, and Output.
The threshold determines the dB level at which your signal will start to be compressed. The lower you set the threshold, the more signal you will be letting through to be compressed. Anything below the threshold will remain uncompressed. After setting your threshold, you need to set the ratio, which is the amount of the signal that will be compressed above the threshold. For instance, a ratio of 4:1 will compress the signal above the threshold, so for every 4 dB of the signal allowed through, the compressor will only output 1 dB.
The attack refers to how quickly the compressor will engage once the signal has crossed the threshold. The quicker your attack, the quicker compression will kick in, and the gain of your signal will be reduced. Some compressors also come with a knee function, which allows the compressor to anticipate when the signal will cross the threshold to be compressed. This allows for the compression to be softened slightly, so it is not such a harsh transition between compressed and uncompressed signals.
The release refers to how quickly the compressor backs off of the signal, allowing it to return to its full gain level as specified by the threshold. Often times setting a quick attack with a slower release works best as it provides a smooth transition between compression and normal signal levels. Otherwise, you could experience noticeable fluctuations in the compressor engaging and disengaging the signal, known as pumping and breathing, both of which are bad.
The last 2 settings on most compressors are Input and Output. Input refers to the amount of signal you are sending through the compressor, and Output is the amount of signal that is leaving the compressor.
Things to Remember:
Input: The amount of signal entering your compressor.
Output: The amount of signal leaving from the compressor to the next stop in your signal flow.
Threshold: determines at which db level your signal will start to be compressed.
Ratio: the amount the signal will be compressed after the signal reaches the threshold.
Attack: the amount of time after exceeding the threshold the transient is allowed to pass through. The quicker the attack, the quicker the gain will be reduced to the specified level.
Release: release refers to how quickly the compressor backs off, allowing the signal to return to full gain as specified by the threshold.