Orban OPTIMOD-FM 5500 Operation Manual page 159

OPTIMOD-FM DIGITAL
terial will be frequency-shifted upon demodulation, and will no longer
bear a harmonic relationship to the material that produced them.
Mathematically, these harmonics will be located at the same frequencies
as harmonics caused by clipping in a simple digital-domain clipper (with
no anti-aliasing) operating at 38 kHz sample rate.
If you want to use the composite limiter more heavily, one option is to
trade off composite limiting against left/right domain overshoot com-
pensation. To do this, reduce the O
and increase the COMP DRV control setting proportionately. (The
O
VERSHOOT
Remote software.)
Overshoot Compensator Drive sets the drive level into the overshoot compensa-
tor with reference to the final clip threshold, in units of dB. The normal setting is "0
dB."
The overshoot compensator can produce audible distortion on material with strong
high frequency content (like bell trees), and this control lets you trade off this dis-
tortion against loudness. (Such material can cause strong overshoots, forcing the
overshoot compensator to work hard to eliminate them.) We do not recommend
operating this control above "0" because this would reduce the effectiveness of the
distortion cancellation used in earlier processing. However, you can reduce it below
"0" if you value the last bit of high frequency cleanliness over loudness.
The overshoot compensator works at 256 kHz sample rate and is fully anti-aliased.
MPX POWER OFFSET operates only when the ITU-412 multiplex power controller is
active (and is thus irrelevant to users in countries that do not enforce this standard).
See ITU-R Multiplex Power Controller on page 3-53. The control introduces a fixed
loss before the FM analog peak limiting chain. If the M
control (in the I
NPUT
control produces the same amount of loss (in dB) as this control's setting. Resetting
the M P
ULTIPLEX OWER
ample, setting the M
decrease by 3 dB.)
The M P
ULTIPLEX OWER
Regardless of the setting of the
MPX P
ger than 0 dB.
The MPX P
O
OWER
that the multiplex power controller might produce. These can occur because the ITU
specification does not call for psychoacoustic weighting. The Optimod does not
force the multiplex power controller to dynamically produce all of the required gain
reduction (which could vary widely, depending on the program material). Instead,
the MPX P O
OWER
duction produced by the control is, of course, unchanging and cannot introduce au-
dible artifacts.
The ideal dynamic gain reduction for the multiplex power controller is 2 to 3 dB
with typical program material. However, the actual gain reduction will vary widely
C D
OMPENSATOR RIVE
/O > U
UTPUT TILITIES
T control away from 0 will change the loss. (For ex-
HRESHOLD
P T
ULTIPLEX OWER HRESHOLD
T control can only introduce loss, never gain.
HRESHOLD
O
controls, the resulting gain offset can never be lar-
OWER FFSET
control's purpose is to reduce unnatural loudness variations
FFSET
control produces most of the gain reduction. The gain re-
FFSET
C
VERSHOOT OMPENSATOR
control is accessible only from the 5500 PC
ULTIPLEX
screen) is set to 0, the MPX P
control to +3 will cause the loss to
M P
ULTIPLEX OWER
OPERATION
D control
RIVE
P T
OWER HRESHOLD
O
OWER FFSET
T and
HRESHOLD
3-35