Optimod-AM 9400 V1.2 Operating Manual - Orban

OPTIMOD-AM DIGITAL OPERATION 3-39
There are three independent gating circuits in the 9400. The first affects the AGC,
while the others affect the multiband compressors in the analog AM and HD chains.
Each has its own threshold control.
The multiband compressor gate causes the gain reduction in bands 2 and 3 of a
given multiband compressor to move quickly to the average gain reduction occurring
in those bands when the gate first turns on. This prevents obvious midrange
coloration under gated conditions, because bands 2 and 3 have the same gain.
The gate also independently freezes the gain of the two highest frequency bands
(forcing the gain of the highest frequency band to be identical to its lower
neighbor), and independently sets the gain of the lowest frequency band according
to the setting of the DJ BASS boost control (in the Equalization screen). Thus, without
introducing obvious coloration, the gating smoothly preserves the average
overall frequency response “tilt” of the multiband compressor, broadly maintaining
the “automatic equalization” curve it generates for a given piece of program material.
If the MB GATE THR (Gate Threshold) control is turned OFF, the DJ BASS
control is disabled.
AGC B CPL (“AGC Bass Coupling”) control clamps the amount of dynamic bass
boost (in units of dB) that the AGC can provide. (In V1.0, the unit of measure was
percent.)
The AGC processes audio in a master band for all audio above approximately 200 Hz
and a bass band for audio below approximately 200 Hz. Starting with V1.1 software,
the AGC Master and Bass compressor sidechains operate without internal coupling.
The gain reduction in the Bass audio path is either the output of the Bass compressor
sidechain or the output of the Master band sidechain. The AGC BASS COUPLING
control sets the switching threshold. For example, if the AGC BASS COUPLING control
is set to 4 dB and the master gain reduction is 10 dB, the bass gain reduction cannot
decrease below 6 dB even if the gain reduction signal from the Bass compressor
sidechain is lower. However, the audio path bass gain reduction can be larger than
the master gain reduction without limit. In the previous example, the bass gain reduction
could be 25 dB
The normal setting of the AGC BASS COUPLING control is 0 dB, which allows the AGC
bass band to correct excessive bass as necessary but does not permit it to provide a
dynamic bass boost.
Note that the operation of this control was changed in 9400 V1.2 software to work
as explained above. You may have to tweak this control to achieve the same bass
balance that you had previously with V1.0 software.
AGC METR (“AGC Meter Display”) determines what signal the front-panel AGC
meter displays. MASTER displays the gain reduction of the Master (above-200 Hz)
band. DELTA displays the difference between the gain reduction in the Master and
Bass bands. Full-scale is 25 dB gain reduction.