Orban OPTIMOD-FM 8700, Operating Manual

Page: 247 / 390

OPTIMOD-FM DIGITAL OPERATION
3-77

If you are using a composite output to drive the FM analog side of your transmis-
sion plant, set the stereo encoder’s D
IVERSITY
D
ELAY
control to I
N
. This control is
located in the
C
OMPOSITE
screen.
If you need the shortest possible input-to-output time delay (for example, if you are
driving talent headphones from the off-air feed), defeat the diversity delay on the
output driving the FM analog transmitter by setting the
O
UT
S
OURCE
to FM or
D
IVERSITY
D
ELAY
to O
UT
as appropriate for the output you are using. In this case, the
delay difference between the analog and digital radio outputs will not stay constant
when you recall different presets. This is not important for these applications be-
cause one gives up proper diversity delay (around eight seconds) for the sake of driv-
ing headphones or minimizing the delay in live sports events, which are the two typ-
ical applications where minimum delay is required. When using this setup, be aware
that analog/digital crossfades in HD Radio receivers will sound very bad. Note too
that switching between an MX and non-MX preset will cause about 345 ms of audio
to be repeated or dropped.
HD I/O Setup Controls
Input/Output > HD Digital Radio screen:
Meter Sel determines if the Main Meter screen will display the left and right output
levels of the FM processing (
D
ISABLED
) or the left and right gain reductions of the
digital-channel look-ahead limiter ( E
NABLED
).
The HD look-ahead limiter is not stereo-coupled. This prevents limiting
on one channel from causing audible modulation effects on the other
channel.
HD HF Shelf EQ (Pre/Post) determines whether the HD HF shelving equalizer will be
placed before or after the look-ahead limiter that feeds the HD output.
Diversity Delay (“In/Out”) determines if the composite output receives audio delayed
with respect to the digital radio output. This control applies to both composite out-
puts—you cannot delay one output without delaying the other. This control is in the
C
OMPOSITE
screen.
You can turn the delay on or off for the various outputs via the 8700i’s API (page 2-
53), automation (page 2-42), and GPI remote interface (page 2-61).
Out Source allows you to determine if a given output (analog left/right, AES3 #1,
AES3 #2) emits the FM-processed signal (
FM
), the FM-processed signal with diversity
delay (
FM+D
ELAY
), the low-delay monitor signal (
M
ONITOR
;
for driving talent head-
phones) or the HD-processed signal (
HD
). This versatile control allows you to selec-
tively apply diversity delay to each output as desired.
Diversity Delay Trim allows you to trim the analog FM delay in intervals of one sam-
ple of 64 kHz (15.6 µs) so that the delays of the analog-FM and digital radio chan-
nels are matched at the receiver’s crossfade point. This prevents audible comb filter-
ing during crossfades. The setting of this control is critical to get best results and you
should adjust it to one-sample accuracy.