Operating instructions

OPTIMOD-AM DIGITAL OPERATION
3-49
fatigue. However, this sound may be quite useful for stations that are or-
dinarily heard very softly in the background because it improves intelligi-
bility under these quiet listening conditions. Stations that are ordinarily
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 FAST setting. Using SLOW
preserves more of the source’s frequency balance, making the sound less
dense and fatiguing when the radio is played loudly.
Bx THR
(“Band x Compression Threshold”) controls set the compression threshold in
each band, in units of dB below the final clipper threshold. For the analog AM chain,
we recommend making only small changes around the factory settings to avoid
changing the range over which the MB
CLIPPING control operates. These controls
will affect the spectral balance of the processing above threshold, but are also risky
because they can strongly affect the amount of distortion produced by the back-end
clipping system.
MB GATE
(“Multiband Gate Threshold”) control determines the lowest input level
that OPTIMOD-AM will recognize as program material. It interprets lower levels as
noise or background sounds and causes the multiband compressor to gate, effec-
tively freezing gain to prevent noise breathing.
There are three independent gating circuits in the 9400. The first affects the AGC
and the second affects the analog AM multiband compressor, and the third affects
the HD AM multiband compressor. Each has its own threshold control.
The multiband compressor gate causes the gain reduction in bands 2 and 3 of the
applicable multiband compressor to move quickly to the average gain reduction oc-
curring 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
neighbor), and independently sets the gain of the lowest frequency band according
to the setting of the DJ
BASS boost control (in the Equalization screen). Thus, with-
out introducing 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 mate-
rial.
Note: If the MB GATE THRESH (Gate Threshold) control is turned OFF, the
DJ
BASS control (in the Equalization screen) is disabled.
MB LIM DR (“Multiband Limiter Drive”; analog AM chain only) sets the drive level
to the multiband distortion controlling processing that precedes the final clipping
section. The distortion-controlling section uses a combination of distortion-cancelled
clipping and look-ahead processing to anticipate and prevent excessive clipping dis-
tortion in the final clipper.
Like any other dynamics processing, the distortion-controlling section can produce
artifacts of its own when overdriven. These artifacts can include loss of definition,