Orban OPTIMOD-FM 8600Si, Operating Manual

Page: 181 / 356

OPTIMOD-FM DIGITAL OPERATION
3-15
With the
FM
Æ
HD C
ONTROL
C
OUPLING set to
I
NDEPENDENT
,
there are several ap-
proaches 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 8600Si’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 8600Si includes an ITU-R BS.1770 Loudness Meter and Safety Limiter in the digi-
tal radio processing path. The Safety Limiter should only be activated if the regula-
tory authority in your country requires constraining BS.1770 Integrated Loudness to
a specified threshold. See step 12 on page 2-35.
Input/Output Delay
The sophisticated look-ahead algorithms in the 8600Si have one significant cost—
the input/output time delay is longer than that of an analog processor and can
cause problems if the if an off-air pickup is used to feed talent headphones.
To make intelligent decisions about how to process, the 8600Si needs to look ahead
at the next part of the program waveform. (Slowly changing bass waveforms re-
quire particularly long look-ahead delays.) As digital on-air processing advances fur-
ther 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
8600Si 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
seconds.
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.