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# Compression

Compression is a soft effect that can be used to reduce the dynamic range of an audio signal from an audio segment. When you compress an audio signal, there is less of a difference between the lowest measured gain of the signal and the highest measured gain of the signal. Compression is useful if your audio signal has many different loudness levels that you want to play back at a similar perceived loudness level. For example, when recording voice-overs, you may want to maintain a constant perceived level of loudness in the actor's voice.

You can also compress an audio signal to attenuate portions of the signal that are too loud. For example, if your recording is at a consistent loudness level, but for some reason there is an unwanted peak in loudness level, you can compress the loud portion to give it the same perceived loudness as the rest of the recording.

Because compressing an audio signal could have a drastic effect on the overall dynamic range of the signal, it is not effective in every situation. For example, for a complex recording that has been mixed down from many other audio sources, such as a vocal track with music and sound effects, the audio signal might have complex differences in loudness levels. If you compress a master audio signal such as this, you will lose many of the original qualities of the audio signal. In such cases, it is advisable that you compress the source audio track before mixing down.

If you are editing a pair of mono tracks that you wish to process as stereo tracks, you should merge both tracks into one stereo audio track. This ensures that the same compression is used on both left and right channels. See Creating and Splitting Stereo Audio Tracks.

The Compression soft effect has the following controls.

Control | Values | Description
--- | --- | ---
Threshold | -60 dB - 0 dB | Determines the level above which signals are affected by the compression. Signals below the Threshold are not compressed. Signals above the Threshold are compressed based on the Ratio setting.
Ratio | 1:1 - 20:1 | Defines the amount of gain reduction applied to the signal above the Threshold level. For example, a Ratio of 2:1 means that for every 2 dB the input signal increases, the output signal will only increase by 1 dB. Gain reduction is displayed on the compression meter.
Attack | 0.1 ms - 100 ms | Defines the speed at which the compression is applied once the signal has reached the Threshold level. A fast attack rate means that most of the signal is compressed. A slow attack rate means the early part of the signal will not be compressed. The result is more natural sounding than using a fast Attack.
Release | 10 ms - 1000 ms or Auto | Defines the speed at which the compressed signal returns to its original value when the input signal level goes below the Threshold value. If Auto Release is enabled, the optimal value is automatically set.
Knee Width | 0 dB - 40 dB | Defines the bend in the response curve. A low number gives a sharp angle and a high number gives a wider, rounded edge. A wider (or softer) knee width reduces the audible change from uncompressed to compressed. A higher knee width is most effective for higher ratios where the changeover is more noticeable.
Output Gain | -10dB - 24 dB | Defines the amount of gain to add to the output signal. For example, if you applied a lot of compression to the signal, you may want to add some output gain to set the output signal to its original overall loudness level.
Auto Release |  | When enabled, the optimal Release time is automatically set according to the input signal.
Peak Detection / RMS Detection |  | Select Peak Detection to compress the signal based on the peak levels. Select RMS Detection to compress the signal based on its average level.