Orban OPTIMOD-AM 9300, Operating Manual

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OPTIMOD-AM DIGITAL OPERATION
3-5
sion and limiting to ensure that the received signal will override the noise and inter-
ference over the maximum possible geographical area. It also requires high fre-
quency boost to compensate for the high-frequency rolloff in all AM radios.
The 9300’s
GEN PURPOSE MEDIUM
factory preset at a
L
ESS
-M
ORE
setting of
7
meets
these requirements and provides a sound that is subjectively undistorted even on
high-quality automobile radios. This is the default preset upon initial power-up of
the 9300. You may continue using this preset or choose another preset as you deem
appropriate.
You must also choose a setting of the system bandwidth control for the active Sys-
tem Preset (in System Setup). Depending on whether the bandwidth is 4.5 - 7 kHz or
7.5 - 9.5 kHz, the characteristics of any factory preset will change to complement the
chosen bandwidth. For example, if the frequency is set at 7.5 kHz or above, the
HF
C
URVE
of the
GEN PURPOSE MEDIUM
preset will be automatically set to
10
and the
HF G
AIN
will be set to +10dB. If the frequency is set at 7.0 kHz or below (as appropri-
ate for areas such as Europe and Asia), the
HF C
URVE
will be set to 0 and the
HF G
AIN
will be set to +17dB. This matches OPTIMOD-AM's HF preemphasis to the bandwidth
of the radios that will most likely be in use in a given part of the world.
If the amount of transmitter power available is limited and you wish to cover the
widest possible area, you may choose to process harder (by advancing the
L
ESS
-
M
ORE
control at the cost of some audible distortion and increased compression). You
may also wish to reduce the amount of high frequency receiver equalization and/or
decrease the audio bandwidth of the processing (by adjusting the system low-pass
filter) because you will discover that you can achieve a louder sound with the same
amount of distortion if you do this.
You will find out that in any setup there is a direct trade-off between loudness,
brightness, and distortion. You can improve any single parameter, but only at the
expense of one or both of the other two. This is true of any processor, not just
OPTIMOD-AM. Perhaps the most difficult part of adjusting a processor is determin-
ing the best trade-off for a given situation. If most of your listeners are located
where your signal is strong, it is wiser to give up ultimate loudness to achieve
brightness and low distortion. A listener can compensate for loudness by simply ad-
justing the volume control. But there is
nothing the listener can do to make a dirty
signal sound clean again, or to undo the effects of excessive high-frequency limiting.
If processing for high quality is done carefully, the sound will also be excellent on
small radios. Although such a signal might fall slightly short of ultimate loudness, it
will tend to compensate with an openness, depth, and punch (even on small radios)
that cannot be obtained when the signal is excessively squashed. On the other hand,
if many listeners receive a weak signal or one that is frequently contaminated by in-
terference, then processing harder to achieve maximum loudness, uniformity, and
average modulation will let the station be heard more easily. You may therefore
wish to process quite differently during the day than at night, when skywave inter-
ference is often a problem. OPTIMOD-AM's programmable presets make this easy.
If women form a significant portion of the station's audience, bear in mind that
women are more sensitive to distortion and listening fatigue than men are. In any