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OPERATION ORBAN MODEL 8685
run the AGC with fast release times without adding excessive density to material
that is already dense.
The AGC contains a compression ratio control that allows you to vary the ratio be-
tween 2:1 and essentially ∞:1. Lower ratios can make gain riding subtler on critical
formats like classical and jazz.
The AGC has its own silence-gating detector whose threshold can be set independ-
ently of the silence gating applied to the multiband compressor.
The 2.0 AGC can be operated in left/right or sum-and-difference mode. You can set
the coupling of the 2.0 AGC’s two sidechains (left/right or sum-and-difference) any-
where from 100% stereo coupled to fully independent.
The surround AGC is always 100% stereo coupled. Its sidechain responds to the
power sum (r.m.s. sum) of all inputs except for LFE channel.
The LFE channel is excluded to prevent the LFE energy from audibly
modulating the loudness of energy at higher frequencies. However, the
gain of the LFE channel follows the gain of the AGC Bass band to keep it
in balance with the rest of the spectrum.
The SURROUND OPTIMIZATION control for the active preset determines how the rear
channels are weighted:
• S
URROUND weights the rear channels 1.5 dB higher than the front channels to
compensate for the ear’s greater sensitivity to the loudness of these channels
when reproduced in surround.
• S
TEREO weights the rear channels 3.0 dB lower than the front channels to reflect
the fact that the default surround > stereo downmix contains each rear channel
mixed at –3 dB.
• C
OMPROMISE weights the rear channels half way between SURROUND and STEREO.
Equalization
The 8685 has a steep-slope bass shelving equalizer and three bands of fully paramet-
ric bell-shaped EQ.
You can set the slope of the bass shelving EQ to 6, 12, or 18 dB/octave and adjust the
shelving frequency.
The 8685’s bass, midrange, and high frequency parametric equalizers have curves
that were modeled on the curves of Orban’s classic analog parametrics (like the
622B), using a sophisticated and proprietary optimization program. The curves are
matched to better than 0.15dB. This means that their sound is very close to the
sound of an Orban analog parametric. They also use very high quality filter algo-
rithms to ensure low noise and distortion.
The 8685 HF Enhancer is a program-controlled HF shelving equalizer that intelli-
gently and continuously analyzes the ratio between broadband and HF energy in
the input program material. It can equalize excessively dull material without over-
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