Digital Output - Orban OPTIMOD-FM 8500S Operating Manual

3-68
OPERATION

Digital Output

are always set "stereo" even when the two audio channels carry identical
mono signals.
HD Bandwidth sets the audio bandwidth of the HD output from 15 to 20 kHz in
1 kHz steps.
The user should carefully test the codec in use to ascertain if lowering the
bandwidth to 15 kHz improves subjective quality. This can occur because
the codec then uses all of its bits to encode information in the most sub-
jectively important part of the ear's bandwidth. If the codec employs
Spectral Band Replication® technology (as does the iBiquity HD Codec),
then you can set the bandwidth at 20 kHz without quality penalty, al-
though the difference between 15 and 20 kHz is unlikely to be audible
following the encode / decode cycle.
HD Polarity sets the polarity of the output of the HD processing to P
. The switch allows you to match the polarity (sometimes informally called
N
EGATIVE
"phase") of the audio through the analog FM and HD transmission channels, re-
gardless of how your facility is configured. It is important to match polarity to avoid
a momentary decrease in loudness during analog/digital receiver crossfades.
This control is best adjusted by observing an HD radio. Using a variable RF attenu-
ator, vary the RF level feeding the radio to force crossfades. If you have correctly ad-
justed the 8500S's A
NALOG
nels, the incorrect setting of the HD P
momentary loudness decrease during the crossfades.
The HD P control can make it easier to match the analog and HD channel de-
OLARITY
lay in an HD Radio installation. Temporarily set this control to cause a null, sum the
HD and FM channels, and adjust the HD D
This works best if the HD and FM analog loudnesses are matched; use the HD L
control to do this.
D
RIVE
If your facility has two FM analog exciters. one of which inverts polarity and one of
which does not, you can use the 8500S's FM P
switching between transmitters. (See step 8 on page 2-29.) This function can also be
controlled via the 8500S's clock-based automation (see page 3- 36).
The AES1 digital output is normally used to drive the digital transmitter. However,
you can use any output (A
following controls, located in the I
Out Level ("Digital Output 1" and "Digital Output 2") sets the digital-channel out-
put level with respect to digital full scale. It is normally set at 0 dBFS, which uses all
the headroom available in the HD transmission channel. To match the loudness of
the analog and digital channels at the receiver, use the L
minimizes the amount of peak limiting necessary to match the loudness of the ana-
log and digital channels at the receiver.
When the BS.1770 Safety Limiter is active, it changes the way the O
trol operates. See step 12 on page 2-35.
C D to time-align the analog and digital chan-
HANNEL ELAY
control should be clearly audible as a
OLARITY
ELAY
OLARITY
L/R, AES1, and AES2). The digital outputs have the
NALOG
/ O screen.
NPUT UTPUT
ORBAN MODEL 8500S
control to achieve the deepest null.
control to compensate when
D
IMITER RIVE
UTPUT
or
OSITIVE
IMIT
control. This
con-
L
EVEL