2 3
The Compressor Threshold controls the point above which the compressor
begins to reduce the gain. For compression, the Compressor Threshold is set
low, so that even low level signal will activate the compression. For limiting,
the Compressor Threshold is set high so that all of the dynamics of the signal
are preserved, but extremely high levels are reduced to protect amplifiers,
speakers, or to prevent tape saturation. In this application, the detector
ignores signal level changes below the threshold.
The 866 features a "soft knee" compression curve for more natural sounding
compression. This means that as the signal level approaches the threshold
setting, the compressor starts to react. The ratio, or slope, of the gain reduc-
tion continues to increase gradually as the signal passes above the threshold
until it reaches the final gain slope set by the Ratio control. This feature
makes the compressor's operation less obtursive by easing into full com-
pression. As you increase the compression Ratio, the "knee" gets sharper, and
the gain reduction increases more rapidly with increased signal. Protective
limiting requires a high compression Ratio setting, so that full compression is
reached quickly.
The time it takes for the detector to react to an increase in signal level is deter-
mined by the Attack control setting. To preserve some of the transient punch
of a signal, the Attack time should be set fairly high. This allows the user to
compress the overall dynamic range of a signal while still preserving the nat-
ural, open feel of the sound. For limiting, the Attack time should be short, so
that potentially damaging transients don't get past the limiting protection of
the compressor.
Release time is the opposite of attack time. The Release time setting deter-
mines the amount of time the detector takes to react to a decrease in signal
level and to release the action of the compression. Faster release times will
help preserve the original dynamics of the signal, but may cause a problem in
some program material. This effect is called "pumping" or "breathing" . As the
compressor lets go of the signal, the level of the signal (and the noise floor)
is allowed to rise. When the next transient hits, the signal level is pushed
down again according to the Attack time setting. Breathing can be minimized
using longer Release times, which smooth out the action of the compressor.
Once a signal has crossed the threshold, the compressor must be told how
much to reduce the gain. The Ratio control determines the amount of gain
reduction, expressed as a ratio, adjustable from 1:1 (no gain reduction) to
∞
:1
(the signal is not allowed to rise above the Threshold level). Compression
ratios express the ratio between the input signal level and the desired output
level. A compression ratio of 2:1 means that for an increase of 2dB above the
threshold input signal, the compressor output will rise only 1 dB. At a ratio of
5:1, an input increase of 5dB above the threshold will yield an output increase
of 1 dB, and so forth. The setting of the Ratio control is dependent upon the
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