FXAlg #950: HardKneeCompress ¥ FXAlg #951: SoftKneeCompress
Algorithm Reference-140
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 over-shoot
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.
For typical compressor behavior, the attack time is considerably shorter than the release time. At very short attack
and release times, the compressor is almost able to keep up with the instantaneous signal levels and the algorithm
will behave more like distortion than compression. In addition to the attack and release times, there is another time
parameter: ÒSmoothTimeÓ. The smoothing parameter will increase both the attack and release times, although the
effect is significant only when its time is longer than the attack or release time. Generally the smoothing time should
be kept at or shorter than the attack time.
You have the choice of using the compressors in feed-forward or feedback configuration. For feed-forward, set the
FdbkComprs parameter to ÒOutÓ; for feedback compression, set it to ÒInÓ. The feed-forward configuration uses the
input signal as the side-chain source. The feedback compressor on the other hand uses the compressor output as the
side-chain source. Feedback compression tends to be more subtle, but you cannot get an instant attack.
In the feed-forward configuration, the signal being compressed may be delayed relative to the side chain
compression processing. The delay allows the signal to start being compressed just before an attack transient
arrives. Since the side chain processing ÒknowsÓ what the input signal is going to be before the main signal path
does, it can tame down an attack transient by compressing the attack before it actually happens. In the feedback
configuration, the delay affects both the main signal and the side chain, and so is of limited usefulness.
A meter is provided to display the amount of gain reduction that is applied to the signal as a result of compression.
Parameters:
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In/Out
When set to ÒInÓ the compressor is active; when set to ÒOutÓ the compressor is
bypassed.
Out Gain
Compressing the signal causes a reduction in signal level. To compensate, the output
gain parameter may be used to increase the gain by as much as 24 dB. Note that the Out
Gain parameter does not control the signal level when the algorithm is set to ÒOutÓ.
In/Out
In or Out
Out Gain
Off, -79.0 to 24.0 dB
FdbkComprs
In or Out
Atk Time
0.0 to 228.0 ms
Ratio
1.0:1 to 100:1, Inf:1
Rel Time
0 to 3000 ms
Threshold
-79.0 to 0.0dB
SmoothTime
0.0 to 228.0 ms
MakeUpGain
Off, -79.0 to 24.0 dB
Signal Dly
0.0 to 25.0ms
Reduction
-dB 40 20 12 8 6 4 2 0
