OPTIMOD-FM DIGITAL
OPERATION
3-35
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-
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
VERSHOOT
C
OMPENSATOR
D
RIVE
control
and increase the
COMP
DRV
control setting proportionately. (The
O
VERSHOOT
C
OMPENSATOR
D
RIVE
control is accessible only from the 8300 PC
Remote software.)
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).
The control introduces a fixed loss before the FM analog peak limiting chain. If the
M
ULTIPLEX
P
OWER
T
HRESHOLD
control (in the
I
NPUT
/O
UTPUT
/
U
TILITIES
screen) is set to
0
, the
MPX
P
OWER
O
FFSET
control produces the same amount of loss (in dB) as this
control’s setting. Resetting the
M
ULTIPLEX
P
OWER
T
HRESHOLD
control away from
0
will
change the loss. (For example, setting the
M
ULTIPLEX
P
OWER
T
HRESHOLD
control to
+3
will cause the loss to decrease by 3 dB.)
The
M
ULTIPLEX
P
OWER
T
HRESHOLD
control can only introduce loss, never gain.
Regardless of the setting of the
M
ULTIPLEX
P
OWER
T
HRESHOLD
and
MPX
P
OWER
O
FFSET
controls, the resulting gain offset can never be lar-
ger than 0 dB.
The
MPX
P
OWER
O
FFSET
control’s purpose is to reduce unnatural loudness variations
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
OWER
O
FFSET
control produces most of the gain reduction. The gain re-
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
depending on whether the underlying processing preset is “loud” or “quiet.” There-
fore, the appropriate setting of the
MPX
P
OWER
O
FFSET
control depends strongly on
what preset is in use. Accordingly, each preset has its own setting of the
MPX
P
OWER
O
FFSET
, which is a processing parameter like any other in a given preset. Hence, ad-
justments that affect the multiplex power controller appear in two independent
places in the Optimod: The
M
ULTIPLEX
P
OWER
T
HRESHOLD
control is a
system setup
control, while the
MPX
P
OWER
O
FFSET
is
part of the on-air preset
.
Depending on the preset, the
MPX
P
OWER
O
FFSET
control’s setting can vary from 0
dB (no effect) to as much as –9 dB. If you customize a preset in any way (including
using
L
ESS
-M
ORE
)
, you may wish to trim the
MPX
P
OWER
O
FFSET
for that preset so
that the multiplex power controller produces 2-3 dB of indicated gain reduction
with typical program material. This will achieve the maximum on-air loudness that
Summary of Contents for 8300J
Page 1: ...Operating Manual OPTIMOD FM 8300 Digital Audio Processor Version 2 1 Software...
Page 7: ...Operating Manual OPTIMOD FM 8300 Digital Audio Processor Version 2 1 Software...
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Page 247: ...OPTIMOD FM DIGITAL TECHNICAL DATA 6 29...
Page 254: ...6 36 TECHNICAL DATA ORBAN MODEL 8300 CPU Module...
Page 260: ...6 42 TECHNICAL DATA ORBAN MODEL 8300 8300 RS232 BOARD PARTS LOCATOR...
Page 262: ...6 44 TECHNICAL DATA ORBAN MODEL 8300 8300 POWER SUPPLY PARTS LOCATOR...
Page 264: ...6 46 TECHNICAL DATA ORBAN MODEL 8300 8300 I O BOARD PARTS LOCATOR...
Page 270: ...6 52 TECHNICAL DATA ORBAN MODEL 8300 DSP BOARD PARTS LOCATOR DRAWING 32170 000 14...
Page 278: ...6 60 TECHNICAL DATA ORBAN MODEL 8300 8300 DISPLAY BOARD PARTS LOCATOR...
Page 279: ...OPTIMOD FM DIGITAL TECHNICAL DATA 6 61 DISPLAY BOARD...