OPTIMOD SURROUND PROCESSOR OPERATION
3-41
This setting is unique to the preset in which it resides. Regardless of its
setting, the 8685 will not permit the system bandwidth to exceed the
bandwidth set by the M
AX LOWPASS FILTER parameter located I/O Setup.
Phase Rotator determines if the phase rotator will be in-circuit. The purpose of the
phase rotator is to make voice waveforms more symmetrical. Because it can slightly
reduce the clarity and definition of program material, we recommend leaving it O
UT
unless program material is mainly speech, where it may result in cleaner sound be-
cause it can substantially reduce the amount of gain reduction that the 8685’s look-
ahead limiter produces on speech waveforms.
AGC Controls
The AGC is common to the Two-Band and Five-Band structures.
Five of the AGC controls are common to the Intermediate Modify and Advanced
Modify screens, with additional AGC controls available in the Advance Modify
screen, as noted in the following table. Some of the AGC controls are available only
in the 2.0 processing chain because the channels in the surround AGC are always
fully coupled.
AGC Off/On
control activates or defeats the AGC.
It is usually used to defeat the AGC when you want to create a preset with minimal
processing (like a CLASSICAL preset). The AGC is also ordinarily defeated if you are
using a studio level controller. However, in this case it is better to defeat the AGC
globally in System Setup.
AGC Drive
control adjusts signal level going into the slow dual-band AGC, there-
fore determining the amount of gain reduction in the AGC. This control also adjusts
the “idle gain”—the amount of gain reduction in the AGC section when the struc-
ture is gated. (It gates whenever the input level to the structure is below the thresh-
old of gating.)
The total amount of gain reduction in the Five-Band structure is the sum of the gain
reduction in the AGC and the gain reduction in the multiband compressor. The total
system gain reduction determines how much the loudness of quiet passages will be
increased (and, therefore, how consistent overall loudness will be). It is determined
by the setting of the AGC
DRIVE control, by the level at which the console VU meter
or PPM is peaked, and by the setting of the M
ULTIBAND DRIVE (compressor) control.
AGC Release
control provides an adjustable range from 0.5 dB/second (slow) to 20
dB/second (fast). The increase in density caused by setting the AGC
RELEASE control
to fast settings sounds different from the increase in density caused by setting the
five-band’s M
ULTIBAND RELEASE control to FAST. You can trade the two off to produce
different effects.
Unless it is purposely speeded-up (with the AGC
RELEASE control), the automatic
gain control that occurs in the AGC prior to the multiband compressor makes audio
levels more consistent without significantly altering texture. Then the multiband
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