Orban OPTIMOD-FM 8500S Operating Manual Download Page 243

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OPTIMOD-FM DIGITAL

OPERATION

3-79

TTACK

IME

settings in the factory presets have been adjusted with this tradeoff in

mind, but you might prefer to make a different one.

The threshold of the band 1 compressor will also affect bass punch. We recommend
that you carefully study the setting of this control (and the

AND

TTACK

IME

con-

trol) in the various 8500S factory presets before making your own adjustments, so
you can get a feel for how we made the tradeoff between punch and distortion at
the factory. If you set the threshold much above –6 dB, you will typically get some
distortion even on steady-state waveforms (depending on where you have set the

ASS

LIPPER

HRESH

control).

This control

is the primary means of trading off bass punch against IM distortion

caused the bass’ pushing non-bass material into the final clippers. Set it more nega-
tive for less punch but less IM distortion.

There are two bass equalizer sections—the

low bass shelving equalizer

and the

bass parametric equalizer

. The main thing to remember about these sections is

that they are static tone controls that apply coloration equally to all program mate-
rial entering the main dynamics processing section of the 8500S. (They do not affect
the AGC section, being located after it in the signal flow.) Accordingly, the five-band
compressor in the 8500S will attempt to undo any coloration added in the equalizer
setting and will automatically re-equalize the sound to the standard established by
the band threshold controls.

Therefore, to get bass to survive the dynamics processing in the 8500S, it is usually
necessary to apply substantial bass boost to the input by using the equalizer con-
trols. (A small amount of boost will just be "automatically re-equalized" away; check
the factory presets to see what we mean by “substantial.”) Bear in mind that using
large amounts of shelving bass boost (particularly with 12- or 18 dB/octave slopes)
can cause an effective loss of mid-bass because the band 2 compressor will be forced
to produce additional gain reduction.

Another important control that affects bass is the

AND

UTPUT

control. Be-

cause this is located after the dynamics processing, the dynamics processing will not
fight any adjustments you make to this control. However, the downside is that the
bass compressor will not act to prevent excessive drive to the clipping system (and
consequent distortion), so be very careful when boosting this control.

The crossover between band 1 and band 2 is adjustable to 100 Hz, 150 Hz, or 200 Hz
by the

OVER

control. When the crossover is set to 100 Hz, band 1 affects ex-

treme low bass (the kind of bass that small clock and portable radios do

not

repro-

duce), while band 2 affects the mid-bass and lower midrange. Setting the crossover
to 200 Hz will cause more gain reduction to occur below 200 Hz because more en-
ergy is applied to the band 1 compressor. If you now increase the fixed bass boost by
using the

ASS

equalizer with an 18 dB/octave slope and 120 Hz tuning, the net

result will be a dynamic reduction of bass power, typically centered around 160 Hz.
If you use enough low bass boost, there will also be a slight increase in the bass
power below 100 Hz or so. This 160 Hz suck-out can give an extremely solid, punchy
bass sound on radios with good bass response (particularly on radios with subwoof-
ers) but may cause smaller radios to sound thin. (This is the bass formula used in the