Orban OPTIMOD-FM 8600, Руководство по эксплуатации

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OPTIMOD-FM DIGITAL OPERATION
3-15
Simultaneously, this HF rolloff may reduce high frequency artifacts in the relatively
low bite-rate codec used in the iBiquity HD Radio system.
With the
FM

HD C
ONTROL
C
OUPLING
set to
I
NDEPENDENT
,
there are several approach-
es to minimizing brightness and conditioning the signal to work well at low bitrates.
•
Use little or no high frequency boost in the HD equalization and band mix sec-
tions.
•
Set the
HD BAND 4>5 COUPLING
to
100%.
•
Set the
HD B5 THRESH
to match the codec and its bitrate. Adjust the threshold
until you find a good compromise between presence and high frequency codec
artifacts. We find the range from -6.0 to +6.0 dB to be useful.
•
Use a moderate Band 5 attack time. 25 ms works well.
•
If necessary, lower the
HD B4 THRESH
.
See About the 8600’s HD / Digital Radio Processing (starting on page 3-71) for a
complete description of the HD setup and subjective adjustment controls.
BS.1770 Compliance for Digital Radio
The 8600 includes an ITU-R BS.1770 Loudness Meter and Safety Limiter in the digital
radio processing path. The Safety Limiter should only be activated if the regulatory
authority in your country requires constraining BS.1770 Integrated Loudness to a
specified threshold. See step 10 on page 2-32.
Because it only offers processing for analog radio, model 8600FM does
not include a BS.1770 Safety Limiter.
Input/Output Delay
The sophisticated look-ahead algorithms in the 8600 have one significant cost—the
input/output time delay is longer than that of an analog processor and can cause
problems if an off-air pickup is used to feed talent headphones.
To make intelligent decisions about how to process, the 8600 needs to look ahead at
the next part of the program waveform. (Slowly changing bass waveforms require
particularly long look-ahead delays.) As digital on-air processing advances further
and further from its analog roots, this is the inevitable price of progress.
The amount of delay depends on several things. Because of their unprecedentedly
sophisticated processing, “MX” presets introduce delays of approximately 265 ms,
which makes real-time monitoring through headphones impossible for talent. The
8600 offers a low-delay headphone monitoring output to solve this problem, which
also occurs in HD Radio installation where the diversity delay is typically 8-10 sec-
onds.
If a non-MX preset is active, the delay is usually low enough to allow talent to moni-
tor live through headphone although a learning period may be required.