Orban OPTIMOD-FM 8600, Operating Manual

Page: 220 / 397

3-40
OPERATION ORBAN MODEL 8600
prevents the AGC from building up density in material whose level is already well
controlled.
The previous explanation was somewhat simplified. In fact, the window has “soft
edges.” Instead of switching abruptly between time constants, the attack and re-
lease times morph smoothly between the setting of the
W
INDOW
R
ELEASE
control and
the setting of the AGC master release and attack controls.
The normal setting for the
W
INDOW
S
IZE
is 3 dB.
Window Release (see
W
INDOW
S
IZE
above.)
AGC Matrix allows you to operate the AGC in left/right mode or in sum / difference
mode. Usually you will operate in left/right mode. However, sum / difference mode
can give a type of stereo enhancement that is different from the enhancement
modes offered in the 8600’s built-in stereo enhancer. This will only work if you allow
the two channels of the AGC to have different gains. To do this, set the
AGC
M
AX
D
ELT
GR
control greater than zero.
It is unwise to set this control beyond 3 dB. Multipath distortion could in-
crease because the amount of L–R energy builds up excessively. We prefer
using the 8600’s stereo enhancer because its built-in gating circuits pre-
vent over-enhancement.
AGC Ratio determines the compression ratio of the AGC. The compression ratio is
the ratio between the change in input level and the resulting change in output lev-
el, both measured in units of dB.
Previous Orban AGCs had compression ratios very close to
∞
:1, which produces the
most consistent and uniform sound. However, the 8600 compressor can reduce this
ratio to as low as 2:1. This can add a sense of dynamic range and is mostly useful for
subtle formats like classical and jazz.
Bass Thresh determines the compression threshold of the bass band in the AGC. It
can be used to set the target spectral balance of the AGC.
As the
AGC B
ASS
C
OUPLING
control is moved towards 0 dB, the
AGC B
ASS
T
HRESH
control affects the sound less and less.
The interaction between the
AGC B
ASS
T
HRESH
control and the
AGC B
ASS
C
OUPLING
control is a bit complex, so we recommend leaving the
AGC
B
ASS
T
HRESH
control at its factory setting unless you have a good reason
for readjusting it.
Idle Gain . The “idle gain” is the target gain of the AGC when the silence gate is ac-
tive. Whenever the silence gate turns on, the gain of the AGC slowly moves towards
the idle gain.
The idle gain is primarily determined by the
AGC D
RIVE
setting—a setting of 10 dB
will ordinarily produce an idle gain of –10 dB (i.e., 10 dB of gain reduction). Howev-
er, sometimes you may not want the idle gain to be the same as the
AGC D
RIVE
set-
ting. The
I
DLE
G
AIN
control allows you to add or subtract gain from the idle gain set-
ting determined by the
AGC D
RIVE
setting.