Orban OPTIMOD-FM 8700, Руководство по эксплуатации

Страница: 56 / 390

1-26
INTRODUCTION ORBAN MODEL 8700i
The stereo encoder is calibrated so that 100% left or right modulation will provide
100% modulation of the stereo composite signal, including pilot tone, but excluding
any SCA subcarriers.
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 8700i’s left/right analog output is switched to F
LAT
, a de-emphasis filter is
inserted between output of the 8700i’s audio processing and its line output. Thus, as
the frequency of the Test Tone is changed, the level at the 8700i’s line output will
follow the selected de-emphasis curve. In most cases, the preemphasis filter in the
driven equipment will undo the effect of the 8700i’s internal de-emphasis, so the
8700i’s output level should be adjusted such that the tone produces 100% modula-
tion 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
appearing at the 8700i’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 earli-
er in the system. It will also pass program material, applying no gain reduction or
protection against overmodulation. It can transparently pass any line-up tone ap-
plied 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 pre-
senter’s headphones. When an “MX” preset is active, the delay through the 8700i
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 “Multipath
Mitigator” phase skew corrector adds about 250 ms of delay.
The 8700i 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 8700i’s low-delay “monitor” output to drive talent headphones.