Shrill, Harsh Sound; Dull Sound - Orban OPTIMOD-FM 5500 Operation Manual

OPTIMOD-FM DIGITAL
must have symmetrical group delay around the carrier frequency. An incorrectly
tuned transmitter can exhibit an asymmetrical passband that will greatly increase
crosstalk into subcarriers.
Amplitude modulation of the carrier that is synchronous with the program ("syn-
chronous AM") can cause program-related crosstalk into subcarriers. Synchronous
AM should be better than 35 dB below 100% modulation as measured on a syn-
chronous AM detector with standard FM de-emphasis (50s or 75s).
The subcarrier receiver itself must receive a multipath-free signal, and must have a
wide and symmetrical IF passband and a linear, low-distortion FM demodulator to
prevent program-related crosstalk into subcarriers.
If the 5500 is in stand-alone stereo generator mode, it is easy to accidentally drive its
internal processing into clipping by applying too much level to the input while rely-
ing on the overshoot limiter and/or composite limiter to limit modulation to 100%.
In addition, if the input signal has not been band-limited to 19 kHz or less, this can
cause aliasing between the stereo main and subchannels. You can eliminate this
aliasing (at the cost of overshoot, which the 5500's overshoot limiter can remove) by
activating the input lowpass filter (step 5 on page 2-24).
See Setup for Stand-Alone Stereo Encoder Mode on page 2-22.

Shrill, Harsh Sound

If you are using the Five-Band structure, this problem can be caused by excessive HF
boost in the HF Equalizer and HF Enhancer. It could also be caused by an excessively
high setting of the BAND 4 THRESH control, or by excessively high settings of the
BAND 4 MIX and BAND 5 MIX controls (located in Intermediate and Advanced Mod-
ify).
If you are driving an external stereo encoder with built-in pre-emphasis, you must
set the 5500's output to Flat in the System Setup > Output screen to prevent double
pre-emphasis, which will cause very shrill sound (and very poor peak modulation
control).
You will always achieve better peak control by defeating the pre-emphasis and in-
put filters of an external stereo encoder, permitting the 5500 to perform these func-
tions without overshoot. Section 1 of this manual contains a detailed explanation of
these, and other, system design considerations.

Dull Sound

If you are using the Two-Band structure, dull-sounding source material will sound
dull on the air. The Five-Band structure will automatically re-equalize such dull-
sounding program material to make its spectral balance more consistent with other
program material.
If the 5500's output is set to Flat in System Setup > Output, there will be no pre-
emphasis unless it is supplied somewhere else in the system. This will cause very dull
sound.
TROUBLESHOOTING
5-5