OPTIMOD-FM OPERATION
3-45
achieved—no further increase in short-term density occurs as more gain re-
duction is applied. This avoids the unnatural, fatiguing sound often produced
by processors at high gain reduction levels and makes OPTIMOD-FM re-
markably resistant to operator gain-riding errors.
2B Gate Thresh (Threshold) control determines the lowest input level that OPTIMOD-
FM recognizes as program; lower levels are considered to be noise or background sounds
and will cause the AGC or two-band compressor to gate, effectively freezing gain to pre-
vent noise breathing.
There are two independent gating circuits in the 8400. 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 and the AGC gain reduction
will eventually recover to –10 dB even when the compressor gate is gated. However, re-
covery is slow enough to be imperceptible. This avoids OPTIMOD-FM’s getting stuck
with a large amount of gain reduction on a long, low-level musical passage immediately
following a loud passage.
It is common to set the
2B Gate Thresh control to –40. Higher settings are primarily use-
ful for radio drama, outside sports broadcasts, and other non-musical programming that
contain ambiance, low-level crowd noise and the like. Slightly higher settings may in-
crease the musicality of the compression by slowing down recovery on moderate-level to
low-level musical passages. When such passages cause the gate to cycle on and off, re-
covery time will be slowed down by the ratio of the “on-time” to the “off time.” This ef-
fectively slows down the release time as the input gets quieter and quieter, thus preserv-
ing musical values in material with wide dynamic range (classical music for example).
2B Bass Coupling
control is used to set the balance between bass and the rest of the fre-
quency spectrum.
The two-band compressor processes audio in a master band for all audio above approxi-
mately 200 Hz, and a bass band for audio below approximately 200 Hz. The
2B Bass
Coupling
control determines how closely the on-air balance of material below 200 Hz
matches that of the program material above 200 Hz.
Settings toward 100% (wideband) make the output sound most like the input. Because
setting the
2B Bass Coupling control at 100% will sometimes cause bass loss, the most
accurate frequency balance will often be obtained with this control set between 70% and
90%. The optimal setting depends on the amount of gain reduction applied. Adjust the
2B
Bass Coupling
control until the band 1 and band 2 Gain Reduction meters track as closely
as possible.
With the
2B Release (Two-Band Release) control set to 2 dB/second, setting the 2B Bass
Coupling
control toward 0% (independent) will produce a sound that is very open, natu-
ral, and non-fatiguing, even with large amounts of gain reduction. Such settings will pro-
vide a bass boost on some program material that lacks bass.
With fast release times, settings of the
2B Bass Coupling toward 100% (wideband) do not
sound good. Instead, set the
2B Bass Coupling control toward 0% (independent). This
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