OPTIMOD-FM DIGITAL TROUBLESHOOTING
5-7
Do not match levels by adjusting the output level of the output driving the HD ex-
citer. Only use this control to match the peak levels of the Optimod output to the
exciter. In other words, if the exciter is set to clip when it receives at –3 dBfs, adjust
the Optimod output level to –3 dBfs. This uses all of the headroom available in the
transmission channel, minimizing the amount of look-ahead limiting that the Opti-
mod needs to do.
Loudness Drops Momentarily During HD Radio Analog/Digital Crossfades
The
analog and digital channels in your transmission path have reversed polarity
with respect to each other and a phase cancellation is occurring in the radio during
crossfades. You can correct this with the HD
POLARITY or FM POLARITY controls. See
page 3-67.
HD Frequency Response is Limited to 15 kHz
The HD
BANDWIDTH control might be set to 15 kHz. See page 3-67.
Even if the
HD BANDWIDTH control is set to 20 kHz, bandwidth will be limited to 15
kHz if the HD output’s sample rate is set to 32 kHz and/or if the sample rate of the
audio applied to the 8500’s digital input is 32 kHz. 20 kHz response requires sample
rates to be set to 44.1 kHz or higher.
You Cannot Set Any Output to Emit an HD Signal
From the main menu, Locate
to S
YSTEM SETUP > DIAGNOSTICS to see if your unit is an
8500FM. The 8500FM is the same as the 8500 except that the 8500FM does not pro-
vide digital radio processing. The 8500FM can be upgraded to an 8500 in the field by
installing the plug-in control module contained in the 8500UPG/HD upgrade kit,
which can be purchased from your Orban dealer.
General Dissatisfaction with Subjective Sound Quality
The
8500 is a complex processor that can be adjusted for many different tastes. For
most users, the factory presets, as augmented by the gamut offered by the L
ESS-
M
ORE control for each preset, are sufficient to find a satisfactory “sound.” However,
some users will not be satisfied until they have accessed other Modify Processing
controls and have adjusted the subjective setup controls in detail to their satisfac-
tion. Such users must fully understand the material in Section 3 of this manual to
achieve the best results from this exercise.
Compared to competitive processors, the 8500 offers a uniquely favorable set of
trade-offs between loudness, brightness, distortion, and build-up of program den-
sity. If your radio station does not seem to be competitive with others in your mar-
ket, the cause is usually source material (including excess use of lossy digital com-
pression), overshoot in the transmission link (including the FM exciter) following the
8500, or an inaccurate modulation monitor that is causing you to under-modulate
the carrier. A station may suffer from any combination of these problems and they
can have a remarkable effect on the overall competitiveness of a station’s sound.
Section 1 of this manual provides a thorough discussion of system engineering con-
siderations, particularly with regard to minimizing overshoot and noise.
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