BSS Audio OPAL Series DPR-944 Owner's Manual - Manual (Page 27)

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9.10 Below
threshold meter
The five LEDs of the below threshold meter give an indication of where the
input signal is in relation to the start of compression. The LED marked ‘TH’ is
halfway on all the time and this point represents the threshold point as set by
the threshold control, any signal that exceeds this level will start the
compressor operating. Observation of this meter during operation will give an
instant picture of how close the signal peaks are to being processed. This is
especially useful for live concert work, as signal levels tend to increase during
the course of the show.
9.11 Gain
reduction meter
Once the input signal has exceeded the threshold point, the compressor starts
to operate, and gain reduction will occur. The amount of gain reduction being
used is displayed on the gain reduction meter. Gain reduction is a useful way
of expressing compressor action, as it gives an instantaneous indication of
how much the signal is actually being processed. If, for example, a particular
signal transient exceeds the threshold point by 12dB, and the ratio knob is set
to 2:1, then we would expect the output to have only increased by 6dB.
Therefore the signal is being reduced in level by 6dB as displayed on the
meter.
Only the first 24dB of a possible gain reduction of 35dB is displayed.
Bear in mind that if the parametric filter is being used with a narrow width,
the amount of energy removed from the program could be quite small, and
may indeed not require any adjustment of the gain control. However there
might still be quite a large gain reduction showing. The meter in this instance
is merely showing the level of signal being removed from that narrow band.
If the DPR 944 is being used with the width control in any position other than
out, both the width and frequency controls on each compressor must be in the
same positions for correct operation.