Am Main Menu - Omnia .9 Installation & User Manual

AM PROCESSING

AM Main Menu

The Main Menu contains controls for pre-emphasis, high- and low-pass filters, positive peaks, inverting the input and output,
and for the built-in test generator.
The Pre-emphasis dropdown control allows you choose whether to apply the standard NRSC profile, or no pre-emphasis
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at all.
The High pass dropdown control sets the frequency below which audio will be filtered while the Low pass control sets
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the frequency above which audio will be filtered.
If the symmetry of the incoming program material normally has significant negative peaks, using the Invert Input control
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will invert the signal and help match the input audio to the processor. The Invert Output control works in much the same
way but on the output side to help match the output of the processor with the transmitter.
The Stereo slider enables matrix Mid/Side clipping compliant with C-QUAM Stereo.
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The Positive Peaks slider sets the maximum positive peak level. Due to the nature of AM modulation, it is possible to
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allow higher than 100% modulation for positive peaks, while negative peaks must be kept at or below 100% to prevent
carrier loss. The L-R component of C-QUAM Stereo must be strictly limited to 100% at all times. Omnia.9 meets both
requirements, as shown by the below screen shots of the built in oscilloscope showing the Mid and Side components
separately.
The 100% Modulation slider sets final output modulation reference level for the digital output. Provided that you have
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assigned "AM Digital Output" to a digital output in System – I/O Options – Main Outputs, a red warning message will
appear at the top of the front panel or NfRemote screen if the output is being overdriven, indicating this control (or the
Positive Peak control) should be turned down. Special care must be taken when using C-QUAM Stereo, as 100% refers
to the AM L+R Sum mono modulation, while the actual output channel is L/R separate, meaning that extra head-room
is required – as much as 7.0 dB for C-QUAM Stereo with an aggressive preset, a lot of stereo enhancement, and 125%
positive peaks. It is recommended to select an aggressive preset (Flamethrower) while turning the stereo enhancement
all the way up as you set it up, and after that select the more reasonable preset you actually plan to use.
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