BSS Audio OPAL Series DPR-422 Owner's Manual - Manual (Page 16)

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If set too fast, the overall volume level will jump up and down, exactly
following the peaks above threshold, producing an unpleasant effect.
If set too low, quiet parts of the program immediately following loud transients
will be subjected to ‘breathing’ or ‘pumping’ effects caused by the VCA
releasing its attenuation (or effectively increasing the system gain) during the
quiet program period, when it is not required.
Control Operations
6.6 AUTO
This feature of the DPR-422 is provided to overcome some of the conflicting
setting requirements associated with the attack and release controls. It is
accessed by pressing the AUTO button, whereupon the DPR-422 automatically
adjusts itself to provide the required attack and release time settings, dependant
on the program content. AUTO uses a combined program related attack time
setting and a two part program related release time setting. The two part
program dependant release provides a fast release to restore below threshold
gain as soon as the transient has passed, and a much longer following release
to avoid rapid gain change effects. Note that once AUTO has been selected,
the attack and release controls become inoperative.
Depressing this button enables the two channels of the DPR-422 to be used in
a stereo system, and ensures that there will be no stereo image shifting under
compression or de-essing. The STEREO LINK switch couples the detector
outputs from both channel 1 and channel 2 together, so that both channels
respond equally to the largest signal present. This combined signal is passed
through the THRESHOLD, RATIO, ATTACK, RELEASE and AUTO controls of
channel 1 and is then applied to BOTH the channel 1 and channel 2 VCAs.
Independent operation of the channel GAIN controls is maintained in link
mode, and they must BOTH be set appropriately.
6.7 Stereo Link