OPTIMOD SURROUND PROCESSOR OPERATION
3-75
namics processing, recall the LOOK-AHEAD LIMITER preset. See page 3-26 for
a description of these presets.
C) If you have started with one of the S
OFT KNEE presets, the AGC will already be
O
FF. If you need a very large amount of compression for an application like
processing material intended for in-flight entertainment systems, you can ei-
ther edit the preset to turn the AGC on or start with a preset other than S
OFT
KNEE.
You can turn the AGC off globally for all presets, which is convenient if
you don’t expect to use it in the future. (See step 2 on page 2-20.)
D) Unless you will be using a large amount of compression for special applica-
tions, set the MB G
ATE THRESHOLD to OFF.
In the SOFT KNEE and LOOK-AHEAD LIMITER presets, this is already done.
The multiband gate only works appropriately when the K
NEE and RATIO
controls of all bands are set identically, which is typically true in broad-
cast applications. We recommend turning off the multiband gate if the
individual K
NEE and RATIO settings are unequal.
E) Adjust the 2B DRIVE control (two-band) or MB DRIVE control (five-band) to
achieve the desired amount of multiband gain reduction.
F) Adjust the release time control (2B
RELEASE or MB RELEASE) to achieve the de-
sired compression density.
If you are using the Five-Band structure, you can use the DELTA RELEASE
controls to fine-tune the release time of each band independently.
The release characteristic is always “automatic” (i.e., with program-
dependent time constants) and the R
ELEASE control simply scales this
process. This, combined with multiband operation, makes the compres-
sion remarkably resistant to the usual compressor pumping and squash-
ing.
G) Adjust the ATTACK TIME controls on the individual compressors to trade off
overshoot control against transient punch.
H) Adjust the R
ATIO and KNEE controls in each band to taste.
The RATIO control sets the compression ratio at the threshold of compres-
sion. To achieve a classic soft knee characteristic, set the R
ATIO to 1:1 and
adjust the softness of the knee with the K
NEE control.
The K
NEE control’s setting is the gain reduction in dB at which the com-
pression ratio reaches ∞:1. (See page 3-53 for a description of the R
ATIO,
K
NEE, and BREAKPOINT controls.)
I) After you adjust the RATIO and KNEE controls, adjust the THRESHOLD controls in
the individual bands to achieve the desired amount of gain reduction.
The KNEE control automatically and invisibly changes a given band’s in-
ternal compression threshold to keep the compressor’s output level con-
stant whenever the drive level is high enough to move the gain reduc-
tion into the ∞:1 range. This means that the internal threshold decreases
with softer knee settings (higher settings of the K
NEE control). However,
the indicated threshold the 8685’s user interface does not change. This
behavior ensures that the T
HRESHOLD control alone determines the maxi-
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