BSS Audio OPAL Series DPR-944 Owner's Manual - Manual (Page 26)

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The centre frequency of the band of interest is selected with the frequency
control. Depressing the side chain listen switch makes the operation of this
control audible, aiding its setting on exactly the signals of interest.
9.8 Width
This control is used in conjunction with the frequency control to set the width
of the parametric filter. If the control is set towards the counter clockwise,
narrow end, very fine 'surgery' may be carried out on the program; the effect
becoming more dramatic as the control is advanced clockwise. Moving the
control to the fully clockwise position takes the filter completely out of
circuit, configuring the DPR 944 as a conventional full range compressor.
9.9 Stereo link
Depressing this switch enables the two compressor channels of the DPR 944 to
be used in a stereo configuration and ensures there will be no stereo image
shifting under compression. The stereo link switch couples the detector outputs
from both compressor 1 and compressor 2 together, so that both channels
respond equally to the largest signal present. This combined signal is passed
through the side chain filter, threshold, ratio, release and auto circuit of
compressor 1. It is then applied to both the compressor 1 and compressor 2
VCAs. Independent operation of the channel gain controls is maintained in
link mode, and they must both be set appropriately.
When linked, the compressor 1 below threshold meter shows the combined
compressor 1 & 2 signal. The compressor 2 below threshold meter shows only
signals on compressor 2, providing a visual indication that there is indeed a
signal on compressor 2. Note that the level on the compressor 2 meter can be
changed with the compressor 2 threshold control, although along with the
compressor 2 ratio and release controls, this has no effect on the operation of
the unit. If desired, the compressor 2 threshold control can be set to out, and
there will then be no signal on the compressor 2 below threshold meter. The
gain reduction meters for both compressors indicate the same value, as
controlled from compressor 1.
Control operations - Compressor