Orban OPTIMOD 6200, Operating Manual

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OPTIMOD TROUBLESHOOTING
5-3
If you are using analog inputs, the headroom of the unit's analog-to-digital (A/D) con-
verter must be correctly matched to the peak audio levels expected in your system (using
System Setup). If your peak program level exceeds the peak level you have specified on
setup, the 6200's A/D converter will clip and distort. (See page 2-24).
Audible Noise On-Air
(See also “RFI, Hums, Clicks, or Buzzes” on page 5-2.)
Excessive compression will always exaggerate noise in the source material.
The 6200 reduces this problem with its compressor gate, which freezes the gain of the
AGC and compressor systems whenever the input noise drops below a level set by the
GATE THR
(Gate Threshold) control, preventing noise below this level from being fur-
ther increased.
If you are using the 6200's analog input, the overall noise performance of the system is
usually limited by the overload-to-noise ratio of the analog-to-digital converter used by
the 6200 to digitize the input. (This ratio is better than 100dB.)
It is important to correctly specify the AI CLIP level in the System Setup: Analog I/O
screen to optimize the noise performance available from the analog-to-digital converter.
You should specify the level as the highest peak level that will be presented to the 6200
under normal operation. If, in an attempt to build in a “safety factor” or increase head-
room, you specify a higher level than this, every 1dB of extra headroom that you gain
will be accompanied by a 1dB increase in the 6200's noise floor.
The 6200's AES/EBU input is capable of receiving words of up to 20 bits. A 20-bit word
has a dynamic range of approximately 120dB. The 6200's digital input will thus never
limit the unit's noise performance even with very high amounts of compression.
If an analog studio-to-transmitter link (STL) is used to pass unprocessed audio to the
6200, the STL's noise level can severely limit the overall noise performance of the sys-
tem because compression in the 6200 can exaggerate the STL noise. For example, the
overload-to-noise ratio of a typical analog microwave STL may only be 70-75dB. In this
case, it is wise to use the Orban 8200ST Studio Chassis to perform the AGC function
prior to the STL transmitter and to control the STL's peak modulation. This will optimize
the signal-to-noise ratio of the entire transmission system. An uncompressed digital STL
will perform much better than any analog STL. Section 1 of this manual has a more de-
tailed discussion.
Shrill, Harsh Sound
This problem can be caused by excessively high settings of the
HF GAIN
control. It can
also be caused by excessively high settings of the
B5 THR
(Band 5 Compression Thresh-
old) control. In this case, you are first likely to notice the problem as harsh sibilance on
voice.