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Fig 1.0 Compressor Module Diagram

The Compressor Module allows you to change the dynamics (volume level over time) of a signal. Compressors are generally used to make sounds 'fit together' in a mix, or to smooth out recordings which have uneven volume levels.


Working with the Compressor Module

When to Use a Compressor

Compressors should be used on signals which have too much dynamic range. The compressor can be used to limit the signal to a specific range, which will make it more useful in the context of a song.

Compressors are also used to side-chain different sounds together. Side-chaining is when one signal is used to drive the compressor, and a different signal is sent through the compressor. This causes the second signal to be compressed by the first signal. Producers use this technique either to make room for the first signal (by attenuating other signals) or to provide a feeling of rhythm in the overall mix.

How a Compressor Works

A compressor works by setting a 'Threshold' level. Whenever a signal rises above this threshold, the signal will start to be attenuated. The amount of attenuation applied will be determined by the signal as it exceed the threshold, multiplied by the compressor's 'Ratio'. When the ratio is set higher, more attenuation will be applied.

The 'Attack' and 'Decay' of a compressor will control how quickly the attenuation is applied, and how quickly it is released. Higher values will lead to a compression dynamic that is sluggish, whereas lower values will give faster response times. Be wary, though. Fast response times can introduce artifacts into the signal, especially when applied to basic sounds such as bell-tones or sine-waves.

Connecting the Compressor Module

The Compressor Module provides two typical AudioGL audio connections, which follow typical audio connection rules.

The Compressor Module can be used in Feedback Loops, as described in the Connections article.


Parameter Range Description
0 to 2

This parameter controls the width of the signal before it is compressed. At a level of '1', the stereo signal will be unmodified. At '2', the signal will have a wider stereo mix, and at '0', the signal will be mono.

-60 to 0

This parameter sets the threshold at which the compressor will be activated. Lowering the threshold will cause the compression to be activated at lower volume levels. Once the signal exceeds this threshold (and the ratio is set above '0'), compression will be applied.

0 to 1

This parameter lowers changes the amount of compression that is applied as the signal exceeds the threshold. Turn this value higher to get a heavier compression effect.

1 to 48

This parameter controls how the compression will be applied. Either the full compression ratio can be applied as soon as a signal exceeds the threshold value, or there can be a smooth transition. This transition is referred to as the 'knee' of the compressor. Increasing this parameter will give the knee a smoother shape.

-20 to 100

This parameter controls how quickly compression will be applied to the signal. Higher values will cause the compressor to respond to signals slowly, while lower values will increase the response times. Bear in mind that short response times can have an effect upon the sound of the signal.

-20 to 100

This parameter controls how quickly compression will be removed from the signal as the signal gets quieter. Higher values will cause the compressor to release from signals slowly, while lower values will increase the release times. Bear in mind that short recovery times can have an effect upon the sound of the signal.

-24 to 24

After compression has been applied, it might be necessary to change the volume of the resultant signal. The gain parameter allows you to either increase or decrease the signal level by 24 decibels.

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