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Dynamics Processing 101
To begin to understand dynamics processing, we must first understand what dynamics are. Dynamics, or the
dynamic range of a signal or audio device, is the amount of level between the softest and loudest possible out-
put. Dynamics processing is applied to a signal to manage the changes in level. Various types of processing
units are available to control dynamics including Noise Gates, Expanders, Compressors, Limiters and De-
Essers. All of these processes have a unique effect on a signal, but one common element they share is that in
one way or another they control gain. Some dynamics processors control gain in a subtle way by slightly reduc-
ing how soft and loud a signal is, while others make drastic changes in gain like reducing the signal until it's off.
Applications for dynamics processing can be categorized by two distinct groups; first, to treat a signal that has
an unpredictable dynamic range and make it predictable, and second, to create a "sound" by squeezing out the
dynamic range. Whether used for a live sound application, recording, mixing or mastering, dynamic processors
like the S•com are valuable tools for controlling gain. The following is a basic overview of dynamics processing
and how it is used to improve the quality of recorded and live sound.
COMPRESSOR
A good compressor is one of the most useful tools in live sound and recording. Compressors are used to control
the dynamic range of a signal, which offers a variety of benefits including leveling a signal that's being recorded,
having an instrument sit in the mix, and increasing the loudness of a sound system to name a few. Drastic
amounts of compression will also result in an effect that becomes more of a sound, than just controlling gain. To
understand how a compressor works, it is necessary to become familiar with the basic parameters which include
threshold, ratio, attack time, and release time.
Threshold
Threshold is the level that once the signal exceeds, gain reduction is applied. The normal range of adjustment for
the threshold level is –40 to +20 dBu. If the threshold level is set above the highest level of the signal being sent
to the compressors, the gain reduction is never triggered. Therefore, the compressor is virtually by-passed. If
the threshold level is set very low so that any signal will trigger gain reduction, the compressor is working as an
automatic leveler.
Ratio
The ratio control is used to set the proportion of gain reduction in relationship to the input signal. For example if
the ratio is set to 2:1 and the signal crosses above the threshold level, an increase in level of 2 dB will produce a
1 dB increase in level at the output. A ratio setting of ∞ to 1 means that an infinite amount of input signal is
needed to raise the output level by 1 dB. This means that the output level stays constant even when the input
crosses over the threshold level.
Attack Time
Attack time is the amount of time that a compressor takes to effect the gain reduction after the signal rises above
the threshold level. A well-designed compressor has adjustable attack times ranging from 300 µs (microsec-
onds) to 300 ms (milliseconds). A good compressor will sound smooth as it begins to control the gain regardless
of the attack time.
Release Time
The release time is set to control how long the compressor takes to return the input signal back to its original
level once the signal falls below the threshold level. The acceptable range for release time is from 50µs to 5 sec-
onds. In normal use, faster release times are used for spoken word and longer release times are generally better
for instrumental music.
Auto Attack and Release
Today, sophisticated compressors often incorporate a dynamic or Auto Attack and Release mode. The S•com's
AEG (Auto Envelope Generator) is such a mode which when engaged, automatically adjusts the attack and
release time based on the dynamically changing input signal.
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