Orban OPTIMOD 8685, Руководство по эксплуатации

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OPTIMOD SURROUND PROCESSOR OPERATION
3-51
creating a sense of increasing loudness although peaks are not actually increasing.
At the gain reduction values set by the
2B M
ASTER
B
REAKPOINT
and
2B B
ASS
B
REAKPOINT
controls, the release rate for these bands becomes constant and density
does not increase with additional amounts of gain reduction.
2B Release Shape selects a LINear or EXPonential release shape.
Linear causes the Two-Band compressor to release at a constant number of dB per
second above the
2B B
REAKPOINT
setting and proportionally to the amount of gain
reduction otherwise.
Despite its name,
E
XPONENTIAL
actually offers a reverse-exponential characteristic: It
causes the release to commence slowly and then speed up as it progresses. The
E
XPONENTIAL
shape allows you to create the open sound of a slow release time with
program material whose level is well controlled while permitting the processing to
quickly correct excessively low input levels. We recommend using Exponential for
general-purpose sound-for-picture programming. For program material dominated
by music,
L
INEAR
may be a better choice because Exponential may create unnatural
side effects. (If the 2B Release control is set between about 0.5 and 2 dB/second, an
Exponential release shape should cause no problems even with music.)
Note: The
B
REAKPOINT
controls do nothing when
E
XPONENTIAL
release is chosen.
2B Gate (“2B Gate Threshold”) threshold control determines the lowest input level
that will be recognized as program material by OPTIMOD 8685; lower levels are con-
sidered to be noise or background sounds and will cause the AGC or two-band com-
pressor to gate, effectively freezing gain to prevent noise breathing.
There are two independent gating circuits in the 8685 Two-Band structure. The first
affects the
AGC and the second affects the two-band compressor . Each has its own
threshold control.
The two-band gain reduction will eventually recover to 0 dB (when the
RELEASE
S
HAPE
is set to
L
INEAR
)
or to the setting of the
2B D
RIVE
control (when the
RELEASE
S
HAPE
is set to E
XP
). However, recovery is slow enough to be imperceptible. This
avoids OPTIMOD 8685’s getting stuck with a large amount of gain reduction on a
long, low-level musical passage immediately following a loud passage.
In E
XP
release mode, the two-band gate’s gated gain reduction is the
same as the setting of the 2B D
RIVE CONTROL
, which is similar to the be-
havior of the AGC gate. This is because E
XP
release is mainly useful in
sound-for-picture processing and is used in the
TV 2B G
EN
P
URPOSE
and
TV 2B G
EN
P
URP
+LC
presets. In these presets, the AGC is defeated so that
all gain riding can occur in the two-band compressor. See AGC Idle Gain
on page 3-44 for a more complete discussion.
It is common to set the 2B G
ATE
control between approximately –35 dB and –25 dB.
Higher values are useful in sound-for-picture processing to prevent background
sounds and underscoring from being pumped up, while lower settings are more
common with musical programming.