Orban OPTIMOD-FM 8600, Operating Manual

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INTRODUCTION ORBAN MODEL 8600
The pilot tone stereo system has an interleaving property, which means that the ste-
reo composite modulation is approximately equal to the higher of the left or right
channels.
Because the pilot tone is phase-synchronous with the stereo subcarrier,
the composite modulation will actually increase about 2.7% when the
modulation is changed from pure single-channel to L+R modulation
while the peak audio level is held constant.
When the 8600’s left/right analog output is switched to
F
LAT
, a de-emphasis filter is
inserted between output of the 8600’s audio processing and its line output. Thus, as
the frequency of the Test Tone is changed, the level at the 8600’s line output will fol-
low the selected de-emphasis curve. In most cases, the preemphasis filter in the driv-
en equipment will undo the effect of the 8600’s internal de-emphasis, so the 8600’s
output level should be adjusted such that the tone produces 100% modulation of
the transmission link as measured after the link’s preemphasis filter. At 100Hz,
switching the de-emphasis out or in will have negligible effect on the level appear-
ing at the 8600’s left and right audio outputs.
You can adjust the frequency and modulation level of the built-in line-up tone. You
can use the front panel, the PC Control software, or the opto-isolated remote con-
trol interface ports to activate the Test Tone.
Built-in Calibrated Bypass Test Mode
A
B
YPASS
Test Mode is available to transparently pass line-up tones generated earlier
in the system. It will also pass program material, applying no gain reduction or pro-
tection against overmodulation. It can transparently pass any line-up tone applied to
its input up to about 130% output modulation, at which point clipping may occur.
Monitoring on Loudspeakers and Headphones
In live operations, highly processed audio often causes a problem with the DJ or
presenter’s headphones.
When an “MX” preset is active, the delay through the
8600 can be as much as 270 milliseconds. This delay will be audible as a distinct echo
that almost no one can tolerate in his or her headphones while speaking. The “Mul-
tipath Mitigator” phase skew corrector adds about 250 ms of delay.
The 8600 offers two main solutions to this problem:
•
Using a non-MX preset, which provides the same algorithms and performance as
Optimod-FM 8500.
•
Using the 8600’s low-delay “monitor” output to drive talent headphones.
Because of the need to apply Multipath Mitigator processing equally to
the FM analog and HD processing chains (to ensure seamless crossfades at
the receiver), the Multipath Mitigator is located immediately after the
AGC in the signal path. It therefore adds delay to all presets and to the
monitor output, making it unusable to headphone monitoring. If you
need to use the monitor output to drive headphones, defeat the Multi-
path Mitigator in Setup.