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Chapter 4 Dynamics processors 86
Use Compressor
The following explains how to eectively use the main Compressor parameters.
Compressor Threshold and Ratio
The most important Compressor parameters are Threshold and Ratio. The Threshold parameter
sets the oor level in decibels. Signals that exceed this level are reduced by the amount set as
the Ratio.
The Ratio parameter is a percentage of the overall level; the more the signal exceeds the
threshold, the more it is reduced. A ratio of 4:1 means that increasing the input by 4 dB results in
an increase of the output by 1 dB, if above the threshold.
For example, with the Threshold set at −20 dB and the Ratio set to 4:1, a −16 dB peak in the
signal (4 dB louder than the threshold) is reduced by 3 dB, resulting in an output level of −19 dB.
Compressor envelope times
The Attack and Release parameters shape the dynamic response of Compressor. The Attack
parameter determines the time it takes after the signal exceeds the threshold level before
Compressor starts reducing the signal.
Many sounds, including voices and musical instruments, rely on the initial attack phase to dene
the core timbre and characteristic of the sound. When compressing these types of sounds, you
should set higher Attack values to ensure that the attack transients of the source signal aren’t
lost or altered.
When attempting to maximize the level of an overall mix, it is best to set the Attack parameter to
a lower value, because higher values often result in no, or minimal, compression.
The Release parameter determines how quickly the signal is restored to its original level after it
falls below the threshold level. Set a higher Release value to smooth out dynamic dierences in
the signal. Set lower Release values if you want to emphasize dynamic dierences.
Important: The results of your settings for the Attack and Release parameters depend not only
on the type of source material but on the compression ratio and threshold settings.
Compressor Knee
The Knee parameter determines whether the signal is slightly, or severely, compressed as it
approaches the threshold level.
Setting a Knee value close to 0 (zero) results in no compression of signal levels that fall just
below the threshold, while levels at the threshold are compressed by the full Ratio amount. This
is known as hard knee compression, which can cause abrupt and often unwanted transitions as
the signal reaches the threshold.
Increasing the Knee parameter value increases the amount of compression as the signal
approaches the threshold, creating a smoother transition. This is called soft knee compression.