Orban OPTIMOD-FM 5700i, Operating Manual

Page: 200 / 335

3-36
OPERATION ORBAN MODEL 5700i
The window works by slowing down changes in the AGC gain reduction that are
smaller than the
W
INDOW
S
IZE
. The window has 2:1 asymmetry around the current
AGC gain reduction. For example, if the W
INDOW
S
IZE
is set to 4 dB, the window ex-
tends 4 dB in the release direction and 2 dB in the attack direction.
If the AGC needs to respond to a large change in its input level by making a gain
change that is larger than the window, then the AGC’s attack and release controls
determine the AGC’s response time. However, if the change in input level is smaller
than the window size, the
W
INDOW
R
ELEASE
control determines the attack and re-
lease times. This is usually much slower than the normal AGC time constants. This
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 5700i’s built-in stereo enhancer. This will only work if you al-
low 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 5700i’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 5700i 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 Threshold 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