Orban OPTIMOD-FM 8700, Operating Manual

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3-90
OPERATION ORBAN MODEL 8700i
distortion even on steady-state waveforms (depending on where you have set the
B
ASS
C
LIPPER
T
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 material enter-
ing the main dynamics processing section of the 8700i. (They do not affect the AGC
section, being located after it in the signal flow.) Accordingly, the five-band com-
pressor in the 8700i will attempt to undo any coloration added in the equalizer set-
ting 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 8700i, 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 B
AND
1 O
UTPUT
M
IX
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
B1 / B2 X
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 ener-
gy is applied to the band 1 compressor. If you now increase the fixed bass boost by
using the
L
OW
B
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
two
GREGG presets.) The rest of the presets use the 100 Hz crossover and have
more mid-bass.
Bass Punch in the MX Presets
The MX presets have two controls that allow you to trade off IM distortion against
bass punch:
B
ASS
P
RE
-L
IMITING
and
B
ASS
L
IMITING
. Setting the
B
ASS
P
RE
-L
IMITING
and
B
ASS
L
IMITING
controls closer to “0” preserves more bass energy below 125 Hz but
simultaneously increases IM distortion. Setting these controls away from “0” tends
to reduce energy below 125 Hz (although this is quite program-dependent). When it