SABINE Graphi-Q2 3122-S User Manual
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9.5.2. Compressor/Limiter Adjustments
Output
Output allows you to vary the signal gain after it has been compressed. Without
this control, the output signal level would fall below the input, since the function
of the compressor is to restrict the increase in gain of signals louder than a user-
defined threshold. In effect, Output lets you make up the gain (and then some)
lost by compressing the signal. Note that the Output control operates
regardless of the other compressor/limiter settings, so it can serve as an output
level control for the Graphi-Q. Exercise caution when raising the output level
of the Graphi-Q, as this may have consequences for the equipment down-
stream in the signal chain and your overall gain structure.
Thresh
Thresh sets the threshold at which the compressor begins to affect the signal.
Any signal below this threshold will pass through the circuit with the gain
unaltered (i.e., unity gain), assuming the output gain is not changed from Unity
setting.
Ratio
Ratio is the compression ratio, designated by two numbers separated by a
colon. The first number represents a potential change in gain at the input stage
of the compressor; the second number represents the corresponding change
that will be allowed at the output of the compressor. In other words, a 3:1
compression ratio means that the output signal level (in dB) will rise 1/3 as much
as the gain change at the input level for signal levels that rise above the
threshold. A compression ratio of 4:1 is effectively a limiter; no matter how much
louder the input rises above the threshold, the output level remains unchanged.
Knee
Knee refers to a changing compression ratio as the compression threshold is
approached and exceeded. Most compressors allow a choice of either “hard
knee,” which applies the full compression ratio dynamics control to the signal
immediately as the input level crosses the threshold, or “soft knee,” which
varies the slope of the compression as the threshold is approached and
crossed. Soft knee smooths the onset of the compression.
The Graphi-Q allows a variable, user adjustable knee. The degree of “softness”
is adjustable using the Remote Control Software only, and is variable from 1 to
40 dB. This value refers to the range in dB of the input signal (with the threshold
as the midpoint) over which the slope of the compression will vary.
The lowest knee value (Compressor Figure 1) represents instant full compres-
sion when the input level crosses the threshold. The highest value (40)
represents a soft-knee compression (Compressor Figure 2) that will begin to
gently compress the input signal 20 dB below the threshold, and allow the full
compression ratio 20 dB above, for a total “soft-knee” range of 40 dB.
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Compressor Figure 1: hard knee
Input Level
Compressor: Hard Knee
Compressor: Soft Knee
Input Level
Threshold
Threshold
Output Level
Output Level
Compressor Figure 2: soft knee