Orban OPTIMOD-FM 8700, Operating Manual

Page: 253 / 390

OPTIMOD-FM DIGITAL OPERATION
3-83
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 8700i output driving the HD exciter . This will force you to
use unnecessarily large amounts of limiter gain reduction, which will
waste the “bonus loudness.”
HD “loudness wars” will not only reduce quality but will also cause un-
balanced, obtrusive crossfades between the analog and digital channels
in the radio. To brand your station’s sound, you can choose the precise
coloration you want on the digital channel. You can still take advantage
of all of the artistic choices implicit in stereo enhancer, equalization, and
multiband compression / limiting settings. Yet you do not need to use ex-
cessive peak limiting, which can only reduce quality.
HD De-Ess allows you to mix an adjustable amount of the high frequency limiter
gain control signal into Band 5 of the HD processing only. This control allows you to
reduce the high frequency response of the HD processing channel in a program-
adaptive manner and is intended to reduce strong sibilance (“ess” sounds) that
might otherwise sound obtrusive. Higher (less negative) numbers give more de-
essing action but will also be more likely to reduce “sparkle” with music. If you no-
tice excessive sibilance, we recommend that you start by setting the control at –18.0
and fine-tune it to taste from there. Once you have set the
HD D
E
-E
SS
control to
your liking, save the resulting preset as a User Preset.
The default setting is
–18
, which provides a good compromise between
brightest sound (which would be accomplished by setting the control to
OFF
) and control of high frequency artifacts that low bitrate codecs in-
troduce.
Band 5 in the HD processing chain has its own gain control sidechain that
is independent of the FM processing chain. Therefore, you can activate
the HD Band 5 compressor to either complement or replace the control
that the
HD DE-ESS control provides.
HD Bass Clip Threshold sets the threshold of the HD processing chain’s hard bass
clipper (the only bass clipper mode available in the HD chain) with reference to the
threshold of the HD processing chain’s peak limiter. (See
Bass Clip Thresh on page 3-
50 ). There are two controls, one for music mode and one for speech mode.
HD Bass Clip Shape (See Hard Clip Shape on page 3-52.)
ITU-R Multiplex Power Controller
The ITU-R recommends that the power in the composite baseband signal (including
the pilot tone), integrated over any 60-second interval, not exceed the power in a