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Using the Compressor
The following section explains how to use the main Compressor parameters.
Setting the Compressor Threshold and Ratio
The most important Compressor parameters are Threshold and Ratio. The Threshold sets
the floor level in decibels. Signals that exceed this level are reduced by the amount set
as the Ratio.
The Ratio 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.
As an 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.
Setting Suitable Compressor Envelope Times
The Attack and Release parameters shape the dynamic response of the Compressor. The
Attack parameter determines the time it takes after the signal exceeds the threshold level
before the Compressor starts reducing the signal.
Many sounds, including voices and musical instruments, rely on the initial attack phase
to define 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
differences in the signal. Set lower Release values if you want to emphasize dynamic
differences.
Important: The discussion above is highly reliant on not only the type of source material,
but also the compression ratio and threshold settings.
Setting the 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.
71Chapter 4 Dynamics Processors