OPTIMOD-PC
OPERATION
3-37
make the idle gain track the setting of the
AGC
D
RIVE
control, set the
AGC
I
DLE
G
AIN
control to zero. To make the idle gain 2 dB lower than the setting of the
AGC
D
RIVE
control, set the
AGC
I
DLE
G
AIN
control to –2.
AGC Bass Attack
sets the attack time of the AGC bass compressor (below 200Hz).
AGC Master Attack
sets the attack time of the AGC master compressor (above
200Hz).
AGC Bass Release
sets the release time of the AGC bass compressor.
AGC Crossover
allows you to choose
A
LLPASS
or
L
INEAR
N
O
D
ELAY
modes.
A
LLPASS
is a phase-rotating crossover that introduces one pole of phase rotation at
200 Hz. The overall frequency response remains smooth as the two bands take dif-
ferent amounts of gain reduction—the response is a smooth shelf without extra
peaks or dips around the crossover frequency. The two bands are down 3 dB at the
crossover frequency. However, this mode adds group delay distortion and is there-
fore subtly less transparent-sounding than the
L
INEAR
N
O
D
ELAY
mode.
L
INEAR
N
O
D
ELAY
(Linear-Phase; no delay)
is a phase-linear crossover whose upper
band is derived 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 appear in the frequency response close to the crossover frequency.
It is use-
ful if you need a crossover with low delay and no phase distortion when flat. Its
downside is the possibility of audible coloration when the gains of the two bands
are considerably unequal.
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 OPTIMOD-PC’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.
AGC Max Delta GR
determines the maximum gain difference permitted between
the two channels of the AGC. Set it to “0” for perfect stereo coupling.
This control works the same regardless of whether the AGC operates in
left/right or sum / difference
M
ATRIX
modes, in both cases controlling the
maximum gain difference between the “channels.” Depending on the
M
ATRIX
mode setting, the “channels” will handle left and right signals or
will handle sum and difference signals. When the AGC operates in sum /
difference
M
ATRIX
mode, this control determines the maximum amount
of width change in the stereo soundfield.
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
