Orban OPTIMOD-FM 8600S, Operating Manual

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OPTIMOD-FM DIGITAL OPERATION
3-37
better to defeat the AGC globally in the System Setup screen.
AGC Drive control adjusts signal level going into the slow dual-band AGC and
therefore determines the amount of gain reduction in the AGC. This also adjusts the
“idle gain”—the amount of gain reduction in the AGC section when the structure is
gated. (It gates whenever the input level to the structure is below the threshold of
gating.)
The total amount of gain reduction in the Five-Band structure is the sum of the gain
reduction in the AGC and the gain reduction in the multiband compressor. The total
system gain reduction determines how much the loudness of quiet passages will be
increased (and, therefore, how consistent overall loudness will be). It is determined
by the setting of the
AGC D
RIVE control, by the level at which the console VU meter
or PPM is peaked, and by the setting of the
MB D
RIVE (compressor) control.
Master AGC Release control provides an adjustable range from 0.5 dB / second
(slow) to 20 dB / second (fast). The increase in density caused by setting the
AGC
R
ELEASE control to fast settings sounds different from the increase in density caused
by setting the Multiband’s
MB R
ELEASE control to
F
AST , and you can trade the two
off to produce different effects.
Unless it is purposely speeded-up (with the
MB R
ELEASE control), the automatic gain
control (AGC) that occurs in the AGC prior to the multiband compressor makes audio
levels more consistent without significantly altering texture. Then the multiband
compression and associated multiband clipper audibly change the density of the
sound and dynamically re-equalize it as necessary (booming bass is tightened; weak,
thin bass is brought up; highs are always present and consistent in level).
The various combinations of AGC and compression offer great flexibility:

Light AGC + light compression yields a wide sense of dynamics, with a small
amount of automatic re-equalization.

Moderate AGC + light compression produces an open, natural quality with au-
tomatic re-equalization and increased consistency of frequency balance.

Moderate AGC + moderate compression gives a more dense sound, particularly
as the release time of the multiband compressor is sped up.

Moderate AGC + heavy compression (particularly with a FAST multiband release
time) results in a “wall of sound” effect, which may cause listener fatigue.
Adjust the AGC (with the
AGC D
RIVE control) to produce the desired amount of AGC
action and then fine-tune the compression and clipping with the Five-Band struc-
ture’s controls.
AGC Gate Thresh (Threshold) control determines the lowest input level that will
be recognized as program by OPTIMOD-FM; lower levels are considered to be noise
or background sounds and cause the AGC or multiband compressor to gate, effec-
tively freezing gain to prevent noise breathing.