Orban OPTIMOD-FM 8600, Operating Manual

Page: 259 / 397

OPTIMOD-FM DIGITAL OPERATION
3-79
toggles between corresponding FM and HD tabs (for example, between
C
OMPRESSORS
and
HD C
OMPRESSORS
).
HD EQ Gain determines the depth of high frequency shelving equalization pro-
duced by the parametric HF shelving equalizer, which will be placed either before or
after the digital-channel look-ahead limiter (depending on the setting of the
HD HF
S
HELF
EQ
control in the
I
NPUT
/ O
UTPUT
HD D
IGITAL
R
ADIO
screen).
When placed before the look-ahead limiter, this equalizer is sometimes
useful for reducing the audible disparity between the FM and digital-
channel outputs (although the
HD B
AND
M
IX
controls are probably more
appropriate for this task). The digital-channel output receives no high
frequency limiting or clipping and may therefore be as much as 6 dB
brighter than the FM output. If you wish to reduce this difference to
smooth out the audible difference between the two channels during a
receiver crossfade, you can apply HF rolloff to the digital-channel channel
by ear. Another reason you might want to do this is if the digital-channel
channel sounds excessively bright after you have optimized the 8600’s
tuning for FM. Of course, you can also use the
HD MB B
AND
M
IX
controls
for this purpose, or use these controls in conjunction with the HF shelving
equalizer.
Yet another reason to use HF rolloff in the digital-channel channel is to
reduce codec artifacts at the high frequencies—the familiar “watery”
sound.
When placed after the look-ahead limiter, the shelving EQ can reduce the
effects of codec overshoot.
The parametric HF shelving equalizer can only produce HF rolloff. It can-
not boost.
HD EQ Freq sets the corner frequency of the parametric HF shelving equalizer.
HD Limiter Dr sets the drive level to the digital-channel look-ahead limiter.
When the BS.1770 Safety Limiter is active, you must use the
HD L
IMITER
D
R
control to
set the amount of gain reduction that the BS.1770 Safety Limiter produces. See step
20.C) on page 2-41.
The factory default is
+4
. When the BS.1770 Safety Limiter is active, the
HD L
IMITER
D
R
control will usually need to be set substantially below 0 dB
unless the preset is quiet (like one of the
C
LASSICAL
presets).
When setting up an HD Radio facility, set the
O
UT
L
EVEL
control to 0 dBFS.
Then adjust the
HD L
IMITER
D
RIVE
in the on-air preset to match the loud-
ness of the HD channel to the loudness of the FM channel at the receiver.
In an HD Radio receiver, the HD channel has 5 dB higher gain than the
analog FM channel. Because the digital channel’s loudness must match
the FM channel during receiver crossfades, there is no need to over-
process the HD channel; you can take advantage of the 5 dB of “bonus
loudness” in this channel to do 5 dB less peak limiting compared to the
FM channel.
Do not match the loudness by turning down the Out Level
control of the 8600 output driving the HD exciter . This will force you to
use unnecessarily large amounts of limiter gain reduction, which will
waste the “bonus loudness.”