Optimod-AM 9400 V1.2 Operating Manual - Orban
Optimod-AM 9400 V1.2 Operating Manual - Orban
Optimod-AM 9400 V1.2 Operating Manual - Orban
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OPTIMOD-<strong>AM</strong> DIGITAL TROUBLESHOOTING 5-3<br />
compromising the <strong>9400</strong>’s noise level, we could eliminate a control that<br />
was frequently misadjusted.<br />
If you are using an external processor ahead of the <strong>9400</strong>, be sure it is not clipping or<br />
otherwise causing problems.<br />
The <strong>9400</strong>'s highly processed output puts great demands on transmitter performance<br />
Some transmitters cannot handle the very high average power in the <strong>9400</strong>'s output<br />
Section 1 discusses this in detail<br />
The distortion of tube-type transmitters will increase substantially as the tubes go<br />
flat with use The first thing to go is asymmetrical positive peak capability, so, if it is<br />
impractical to replace the modulator tubes at this time, reduce the setting of the<br />
<strong>9400</strong> POSITIVE PEAK control until the transmitter no longer compresses the peaks. Indeed,<br />
some transmitters cannot handle asymmetrical positive peaks without compression<br />
even with good tubes, Never try to run these transmitters with asymmetry.<br />
The codecs used in the HD <strong>AM</strong> and DRM systems operate a very low bit rates. They<br />
tend to produce more artifacts as program material becomes denser. To prevent the<br />
<strong>9400</strong>’s processing from increasing density excessively, we recommend setting the MB<br />
RELEASE control in the digital radio processing close to SLOW and to use minimal<br />
amounts of look-ahead limiting.<br />
Unfortunately, some CDs are now mastered with so much compression, limiting, and<br />
clipping that they cause codecs to misbehave without further processing in the<br />
broadcast chain. Until the broadcast industry successfully pressures the record industry<br />
to supply broadcasters with lightly processed broadcast-mastered music, this<br />
problem will continue.<br />
Audible Noise on Air<br />
(See also “RFI, Hums, Clicks, or Buzzes” on page 5-1.)<br />
Excessive compression will always exaggerate noise in the source material. The <strong>9400</strong><br />
has two systems that fight this problem.<br />
1. The compressor gate freezes the gain of the AGC and compressor systems whenever<br />
the input noise drops below a level set by the threshold control for the processing<br />
section in question, preventing noise below this level from being further increased.<br />
There are three independent compressor gate circuits in the <strong>9400</strong>. The first<br />
affects the AGC, while the second and third affect the Multiband Compressors in the<br />
<strong>AM</strong> analog and digital radio chains respectively. Each has its own independent<br />
threshold control. (See MB GATE on page 3-49.)<br />
2. The dynamic single-ended noise reduction (see DWNEXP THR on page 3-50) can be<br />
used to reduce the level of the noise below the level at which it appears at the input.<br />
If you are using the <strong>9400</strong>'s analog input, the overall noise performance of the system<br />
is usually limited by the overload-to-noise ratio of the analog-to-digital converter<br />
used by the <strong>9400</strong> to digitize the input. (This ratio is better than 108 dB.) It is