Orban Optimod-PC 1101, Operating Manual

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OPTIMOD-PC OPERATION
3-25
the processor that performs this multiband compression.
All AGC presets use the look-ahead limiter to prevent overloading the STL on peaks.
Compared to
F
LAT
, the 50
μ
S
and 75
μ
S
presets progressively reduce the drive level to
the look-ahead limiter to prevent strong high frequency energy from triggering au-
dible gain pumping or ducking. The high frequency limiting action in the five-band
compressor also helps prevent this artifact.
LOOK-AHEAD LIMITER: The L
OOK
-A
HEAD
L
IMITER
preset is a Two-Band preset that
turns off the stereo enhancer, AGC, equalizer, and two-band compressor so that you
can use the processing as a fast look-ahead protection limiter.
This preset’s L
ESS
-M
ORE
control is set to 1.0. With this setting, there is unity gain
from the input to the output of the audio processing block, which does not include
the Processor Mixer. Even though the gain is unity through the processing block, you
can still use the Processor Mixer to adjust the I/O gain according to your require-
ments.
When L
ESS
-M
ORE
= 1, the threshold of the look-ahead limiter is the same as the Pro-
cessor Mixer’s output clipping level. This means that there can be no look-ahead lim-
iter gain reduction because the Processor Mixer will clip before any gain reduction
could occur. Functionally,
L
ESS
-M
ORE
= 1 bypasses the processing.
This is equivalent to setting the input, threshold, and make-up gain con-
trols of a studio-style protection limiter to “0 dB.”
To produce look-ahead limiter gain reduction, turn up the L
ESS
-M
ORE
control. Each
step of the L
ESS
-M
ORE
control increases the drive level to the look-ahead limiter by
1 dB and increases the input/output gain by 1 dB for signals below the limiter
threshold. At
L
ESS
-M
ORE
= 10 , the processor’s gain below threshold has increased to
9 dB and the input headroom (the difference between the processor mixer clipping
level and the look-ahead limiter threshold) is also 9 dB.
Instead of adjusting L
ESS
-M
ORE
, you could adjust the F
INAL
L
IMIT
D
RIVE
control (which
is what L
ESS
-M
ORE
actually does). The F
INAL
L
IMIT
D
RIVE
control allows you to achieve
up to 12 dB of look-ahead limiting.
Do not set the F
INAL
L
IMIT
D
RIVE
control below “0” with this preset; doing
so will compromise system headroom.
Adjusting the L
ESS
-M
ORE
or F
INAL
L
IMIT
D
RIVE
controls is equivalent to simul-
taneously decreasing the threshold and increasing the make-up gain in a
protection limiter having threshold and output make-up gain controls.
When the output level controls in the I/O Mixer are set to their maximum values, the
look-ahead limiter always constrains the peak level to 0 dBfs at the digital outputs
and to +24 dBu at the analog output, which prevents any output from clipping. To
produce a lower peak level at a given output, turn down the corresponding output
level control in the I/O Mixer. Another use for the output level controls is to produce
unity below-threshold gain between the active input and output, which is some-
times desired in protection limiting applications.