OPTIMOD-FM DIGITAL
OPERATION
3-81
Assuming that the subcarrier and composite signal are uncorrelated and that the
composite signal is limited so that its power is equivalent to a sinewave at 25.3%
modulation, we calculate their R.M.S. sum as follows:
dB
81921
.
11
)
25647
.
0
(
log
20
25647
.
0
0016
.
0
06418
.
0
04
.
0
0.25333
2
2
Recalling that the MPX POWER LEVEL meter is calibrated so that it indicates 0 dB
when the composite output of the 8600S is a sinewave at –11.92615 dB below 100%
modulation, we conclude that our subcarrier at 4% injection will add 0.10694 dB to
the multiplex power. Another calculation (not shown) indicates that 10% injection
will add 0.62889 dB to the MPX power.
Multiplex Power Threshold
Your Optimod provides a means to limit the integrated multiplex power to the ITU
standard by a closed-loop technique that allows you to use any preset and to create
customized presets freely. The multiplex power controller is adjusted via the
ITU412-
9
control (see step 1 on page 2-23
. Set it
OFF
if your country does not enforce the
standard.
The control is located in the
Setup
>
S
TEREO
E
NCODER
screen because the regulation
applies to all operation of the processor in a given installation.
If your country enforces the standard, you should set the control to complement the
amount of peak overshoot in the transmission system following your Optimod. Set-
ting the control at “0” will correctly control the multiplex power when there is no
overshoot after the 8600S. This will typically be true when you are using your Opti-
mod’s built-in stereo encoder to drive the transmitter directly.
Section 1 of this manual has an extensive discussion of overshoot in transmission
paths. See page 1-
Error! Bookmark not defined.
and following pages.
Many paths have overshoot, and this forces you to reduce the average modulation
to avoid overmodulating the transmitter. This would reduce the multiplex power by
the same amount, forcing the multiplex power below the ITU requirement.
To compensate for this, match the
ITU412-9
control to the peak overshoot of the
transmission system following the 8600S. For example, if RF peak deviation exceeds
the peak deviation produced by the 8600S’s sinewave oscillator (set for 100% modu-
lation) by 3 dB, set the
MULTIPLEX
POWER
THRESHOLD
to “+3.”
Audio Processing and the Multiplex Power Threshold Control
Starting with version1.1 software, the multiplex power controller reduces multiplex
power by applying gain reduction after the Optimod’s FM peak limiting system,
which reduces the tendency of the MPX power controller to produce unnatural-
sounding gain reduction because the standard forces MPX power to be measured
after preemphasis and without psychoacoustically weighting.
With no power control, some of the louder 8600S presets can exceed the ITU stan-
dard by as much as 12 dB. This means that the controller must reduce gain by as
Содержание OPTIMOD-FM 8600S
Страница 1: ...Operating Manual OPTIMOD FM 8600S Digital Audio Processor Version 2 1 Software ...
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Страница 254: ...3 88 OPERATION ORBAN MODEL 8600S ...
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Страница 328: ...6 28 TECHNICAL DATA ORBAN MODEL 8600S CONTROL BOARD PARTS LOCATOR ...
Страница 334: ...6 34 TECHNICAL DATA ORBAN MODEL 8600S 5700 8600S I O DSP BOARD PARTS LOCATOR DRAWING 32370 860 01 ...
Страница 339: ...OPTIMOD FM DIGITAL TECHNICAL DATA 6 39 8600S I O BOARD COMPOSITE SCA DAUGHTERBOARD SHEET 4b of 12 62310 000 02 1 ...
Страница 348: ...6 48 TECHNICAL DATA ORBAN MODEL 8600S FRONT REAR FRONT PANEL PARTS LOCATOR DIAGRAM 32275 000 09 ...
Страница 352: ...6 52 TECHNICAL DATA ORBAN MODEL 8600S ...
Страница 353: ...OPTIMOD FM DIGITAL TECHNICAL DATA 6 53 ...
Страница 354: ...6 54 TECHNICAL DATA ORBAN MODEL 8600S ...