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Algorithm Reference
CompressDualTime
3-61
949 CompressDualTime
Compression with 2 release time constants
PAUs:
2
CompressDualTime is a basic compressor with two different release rates, which change from one rate to
another as the compression gain reduction crosses a threshold set by the Rel Thres (release threshold)
parameter. Except for the additional release rate and release threshold parameters, this compressor is like
SoftKneeCompress.
Like a normal compressor, this compressor reduces the gain of a signal as the signal increases above the
compression threshold set with CompThres parameter. The amount of compression is expressed as a ratio.
The compression ratio is the inverse of the slope of the compressor input/output characteristic. The
amount of compression is based on the side chain input signal (left, right or larger of left and right
magnitudes). A compression ratio of 1:1 will have no effect on the signal. An infinite ratio, will compress
all signal levels above the threshold level to the threshold level (zero slope). For ratios in between infinite
and 1:1, increasing the input will increase the output, but by less than it would if there was no
compression. The threshold is expressed as a decibel level relative to digital full-scale (dBFS) where
0 dBFS is digital full-scale and all other available values are negative.
To determine how much to compress the signal, the compressor must measure the signal level. Since
musical signal levels will change over time, the compression amounts must change as well. You can
control the rate at which compression changes in response to changing signal levels with the attack and
release time controls. With the attack time, you set how fast the compressor responds to increased levels.
At long attack times, the signal may overshoot the threshold level for some time before it becomes fully
compressed, while at short attack times, the compressor will rapidly clamp down on the level. The release
time controls how long it takes the compressor to respond to a reduction in signal levels. At long release
times, the signal may stay compressed well after the signal falls below threshold. At short release times,
the compressor will open up almost as soon as the signal drops.
CompressDualTime has a special way of handling the release time. There are in fact two release times: Rel
Time A and Rel Time B. There is also a release threshold (Rel Thres) parameter. While the amount of
compression gain reduction exceeds the release threshold, the release time will be determined by Rel Time
A. As soon as the amount of reduction is less than the threshold, the release time changes to Rel Time B.
You can set the release times so that the release is initially very fast, and then let it slow down when it
crosses the release threshold. Likewise, you can have a very slow release, which suddenly speeds up as
reduction reaches the release threshold. Be sure to watch the reduction meter to follow what is happening
as you change the parameters.
You can select which channel, left (L), right (R) or the maximum amplitude of the two (L & R) is used to
control the compression (side chain processing) with the SC Input parameter. You can also select which
channel is actually compressed, again left (L), right (R) or both (L & R) using the ComprsChan parameter.