Orban OPTIMOD-FM 8700, Operating Manual

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3-66
OPERATION ORBAN MODEL 8700i
band compressor is substantially lower (so that it operates more like a
limiter than like a compressor) and the release time of the gain-riding
AGC is speeded up (so that it provides compression and some increase of
density). We made these trade-offs to prevent excessive build-up of den-
sity.
It is possible to experiment with this sound for music-oriented program-
ming as well. However, even with these settings, your sound is getting
farther away from the balance and texture of the input. We think that
this is as far as processing can go without causing unacceptable listener
fatigue. However, this sound may be useful for stations that are ordinari-
ly heard very softly in the background because it improves intelligibility
under these quiet listening conditions. Stations that are usually played
louder will probably prefer one of the slower release times, where the
multiband compressor takes more gain reduction and where the AGC is
operated slowly for gentle gain riding only. These slower sounds are less
consistent than those produced by the
F
AST
setting. Using
S
LOW
preserves
more of the source’s frequency balance, making the sound less dense and
fatiguing when the radio is played loudly.
The
S
PEECH
MB R
ELEASE
control overrides the
MB R
ELEASE
control when the 8700i
automatically detects speech (page 3-73). You may wish to set the
S
PEECH
MB
R
ELEASE
control faster for speech (to maximize smoothness and uniformity) and
slower on music (to prevent excessive build-up of density).
MB Gate Thresh (Threshold) control determines the lowest input level that will be
recognized as program by OPTIMOD-FM; lower levels are considered to be noise or
background sounds and cause the AGC or multiband compressor to gate, effectively
freezing gain to prevent noise breathing.
There are two independent gating circuits in the 8700i. The first affects the AGC and
the second affects the multiband compressor
. Each has its own threshold control.
The multiband compressor’s gating threshold is set with respect to the signal driving
the multiband compressor/limiter, which follows the AGC. Meanwhile, the AGC gat-
ing threshold remains set with respect to the AGC’s input. Driving the MB gate de-
tector after the AGC allows the AGC to do its work of slowly correcting the drive
level to later processing, including the multiband gate.
The multiband compressor gate causes the gain reduction in bands 2 and 3 of the
multiband compressor to move quickly to the average gain reduction occurring in
those bands when the gate first turns on. This prevents obvious midrange coloration
under gated conditions, because bands 2 and 3 have the same gain.
The gate also independently freezes the gain of the two highest frequency bands
(forcing the gain of the highest frequency band to be identical to its lower neigh-
bor) and independently sets the gain of the lowest frequency band according to the
setting of the
DJ B
ASS
boost control (in the Equalization screen). Thus, without in-
troducing obvious coloration, the gating smoothly preserves the average overall
frequency response “tilt” of the multiband compressor, broadly maintaining the
“automatic equalization” curve it generates for a given piece of program material.