Orban OPTIMOD-FM 5500 Operation Manual page 181

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OPTIMOD-FM DIGITAL OPERATION
allow the bass clipper threshold to be raised during speech, minimizing clipper-
induced speech distortion.
The threshold of the band 1 compressor also affects bass punch. We recommend
that you carefully study the setting of this control (and the B con-
1 A T
AND TTACK IME
trol) in the various 5500 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
BASS CLIP 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 fixed tone controls that apply coloration equally to all program material going
into the main dynamics processing section of the 5500. (They do not affect the AGC
section because they are located after it in the signal flow.) Accordingly, the five-
band compressor in the 5500 will attempt to undo any coloration added in the
equalizer setting and will automatically re-equalize the sound to the standard estab-
lished by the band threshold controls.
Therefore, to get bass to survive the dynamics processing in the 5500, 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 B1 O control, a mixer control
UT
that determines the contribution of band 1 to the total mix of the five bands. Be-
cause this control 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 sys-
tem (and consequent distortion), so be very careful when boosting this control.
The crossover between band 1 and band 2 is adjustable to 100 Hz or 200 Hz by the
control, which you can only access from the 5500 PC Remote software.
B1/B2 X
OVER
When the crossover is set to 100 Hz, band 1 affects extreme low bass (the kind of
bass that is not reproduced by small clock and portable radios), while band 2 affects
the mid-bass and lower midrange. Setting the crossover at 200 Hz will cause more
gain reduction to occur below 200 Hz because more energy is applied to the band 1
compressor. If you now increase the fixed bass boost by using the L equal-
B
OW ASS
izer 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 subwoofers) but may cause smaller