Orban OPTIMOD-FM 8600, Operating Manual

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OPTIMOD-FM DIGITAL OPERATION
3-41
You might want to do this if you make a custom preset that otherwise
causes the gain to increase or decrease unnaturally when the AGC is gat-
ed. For example, to make the idle gain track the setting of the
AGC D
RIVE
control, set the
I
DLE
G
AIN
control to zero. To make the idle gain 2 dB low-
er than the setting of the
AGC D
RIVE
control, set the
I
DLE
G
AIN
control to
–2
.
AGC Bass Attack sets the attack time of the AGC bass compressor (below 200 Hz).
AGC Master Attack sets the attack time of the AGC master compressor (above 200
Hz).
AGC Bass Release sets the release time of the AGC bass compressor.
Master Delta Threshold allows you to set the difference between the compression
thresholds of the sum and difference channels. (This control is only useful when you
set the
AGC M
ATRIX
to
SUM
/
DIF
.) By setting the threshold of the difference channel
lower than the sum channel, you can have the AGC automatically produce more
gain reduction in the difference channel. This will reduce the separation of material
with an excessively wide stereo image (like old Beatles records). To make this work,
you must set the
M
AX
D
ELTA
GR
control away from zero. For example, to limit an ex-
cessively wide image while preventing more than 3 dB difference in gain between
the sum and difference channels, set the
M
AX
D
ELTA
GR
control to 3.0 and the
M
ASTER
D
ELTA
T
HRESHOLD
control to some positive number, depending on how much
automatic width control you want the 8600 to perform.
Bass Delta Threshold works the same as
M
ASTER
D
ELTA
T
HRESHOLD
,
but applies to
the bass band. You will usually set it the same as
M
ASTER
D
ELTA
T
HRESHOLD
.
AGC Crossover allows you to choose
A
LLPASS
,
L
I
N
O
D
LY
, or
L
INEAR
modes.
A
LLPASS
is a phase-rotating crossover like the one used in the 8200’s two-band AGC.
It introduces one pole of phase rotation at 200 Hz. The overall frequency response
remains smooth as the two bands take different degrees of gain reduction—the re-
sponse is a smooth shelf without extra peaks or dips around the crossover frequency.
The two bands are down 3 dB at the crossover frequency.
All Five-Band factory presets automatically use
A
LLPASS
because of its
smooth, shelving behavior and low delay. Its allpass characteristic com-
plements the existing phase rotator that reduces voice distortion. Be-
cause the Five-Band structure uses phase-rotating crossovers in the five-
band compressor / limiter, there is little or nothing to be gained by using
a phase-linear crossover in the Five-Band structure’s AGC.
L
I
N
O
D
LY
(Linear-Phase; no delay) is a phase-linear crossover whose upper band is de-
rived by subtracting its lower band from the crossover’s input. When the upper and
lower bands have the same gain, their sum is perfectly flat with no phase rotation.
However, when the upper and lower bands have different gains, peaks and dips ap-
pear in the frequency response close to the crossover frequency.
L
I
N
O
D
LY
is useful if you need a crossover with low delay and no phase
distortion when flat. Its downside is the possibility of coloration when
the gains of the two bands are widely disparate.