Orban OPTIMOD-FM 5500 Operation Manual page 158

3-34
OPERATION
distortion on speech.
CLIP SHAPE ("Bass Clip Shape") allows you to change shape of the knee of the in-
put/output gain curve of the bass clipper. The "knee" is the transition between no
clipping and flat topping. A setting of "0" provides the hardest knee. "10" is the
softest knee, where the transition starts 6 dB below B
occurs gradually. The factory default setting is "7.6."
FINAL CLIP ("Final Clip Drive") adjusts the level of the audio driving the back end
clipping system that OPTIMOD-FM uses to control fast peaks. This control primarily
determines the loudness/distortion trade-off.
Turning up the F
C
INAL
harder, reducing the peak-to-average ratio, and increasing the loudness on the air.
When the amount of clipping is increased, the audible distortion caused by clipping
also increases. Although lower settings of the F
they make the sound cleaner.
If the R control is set to its faster settings, the distortion produced by the
ELEASE
back-end clipping system will increase as the M
The F and/or the M
C D
INAL LIP RIVE
turned down to compensate. To best understand how to make loudness/distortion
trade-offs, perhaps the wisest thing to do is to recall a factory multiband preset, and
then to adjust the L
ESS
each setting of the L
ESS
and M
L T
ULTIBAND IMIT HRESHOLD
grammers made the trade-offs between the settings of the various distortion-
determining controls at various levels of processing.
The 5500's multiband clipping and distortion control system works to
help prevent audible distortion in the final clipper. As factory program-
mers, we prefer to adjust the FINAL CLIP control through a very narrow
range (typically –0.5 dB to –1.0 dB) and to determine almost all of the
loudness/distortion trade-off by the setting of the Multiband Clipping
control.
The final clipper operates at 256 kHz sample rate and is fully anti-aliased.
COMP DRV ("Composite Limiter Drive") sets the drive level, in dB, into the 5500's
composite limiter.
This control has no effect on the 5500's left and right analog or digital outputs.
The COMP DRV control is set to "0 dB" for most factory presets. At this
setting, it removes a few tenths of a dB of residual overshoot from the
audio processing without affecting audio quality. We prefer to use the
audio-domain overshoot compensation to do most of the work because
it operates at a 256 kHz sample rate and is fully anti-aliased, whereas the
composite limiter will inevitably introduce aliasing around 38 kHz upon
demodulation in the receiver. This is because it introduces spectrum in
the stereo subchannel area when it clips material in the 0 to 15 kHz area.
The receiver will "see" this as stereo material, and will demodulate it as if
it were part of the stereo subchannel. Accordingly, harmonics of L+R ma-
control drives the final clipper and overshoot compensator
LIP
L
ULTIBAND
control to several settings throughout its range. At
-M
ORE
-M control, examine the settings of the M
ORE
controls. This way, you can see how the factory pro-
C T
ASS LIP HRESHOLD
control reduce loudness,
C
INAL LIP
D control is advanced.
ULTIBAND RIVE
controls may have to be
T
IMIT HRESHOLD
ORBAN MODEL 5500
setting and
D
ULTIBAND RIVE