BSS Audio DPR-402 Owner's Manual - Manual (Page 22)

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11.0 Compression meters
Referring back to section 10.1, where we discussed the VCA window of
operation, the five LEDs (See figure 11.1) of the BELOW THRESHOLD meter
will give you an indication of the input signal in relation to this window.
You will notice that the LED marked 'TH' is half-on all the time. This point
represents the threshold point as set by the THRESHOLD control, and any
signal level that exceeds this LED will start the compressor operating.
Rotating the threshold control anticlockwise effectively lowers the window of
the VCA, allowing it to sit at the right point on the input signal. Observation
of this meter during program will give an instant picture of how much of the
input signal is being processed, or how near the peaks are to being processed.
This will provide valuable information at all times during use, especially for
live concert work, where signal levels tend to increase during the course of
the show.
11.1 Below
Threshold and
Gain Reduction
Meter
Fig 11.1 BELOW
THRESHOLD meter
Once the input signal has exceeded the threshold point on scale, the
compressor starts to operate, and gain reduction will occur. The amount of
gain reduction being used is displayed on the GAIN REDUCTION meter (See
figure 11.2).
Fig 11.2 GAIN
REDUCTION meter
Compression Meters
Gain reduction is a useful way of expressing compressor action. We have seen
that the output level of a compressor is less than the input level by some
amount that depends on the threshold, ratio, attack and release time settings.
If, for example, a particular signal transient exceeds the threshold point by
10dB and the ratio knob is set to 2:1, then we would expect the output to have
only increased by 5dB (providing the time controls are set accordingly).
Assuming the gain control is at 0dB, the difference between the input and
output levels of 5dB then represent the amount of gain reduction which has
occurred and will be displayed on the gain reduction meter as 5dB (See figure
11.3).