Orban OPTIMOD-FM 8500S, Operating Manual

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OPTIMOD-FM DIGITAL OPERATION
3-7
About the 8500S’s Signal Processing Features
Dual-Mono Architecture
The 8500S implements full dual-mono architecture in both the AGC and the multi-
band compressor sections. You can couple each band in both the AGC and multi-
band compressors to a variable extent—anywhere from perfect stereo coupling to
completely uncoupled operation. The coupling control determines the maximum
amount of gain imbalance permitted between the left and right channels in a given
band, and therefore the amount of stereo image shift permitted in each frequency
band.
Although the processing is dual-mono, you cannot adjust setup controls independ-
ently on the left and right channels—we assumed that the 8500S would always
process stereo program material.
Signal Flow
The signal flows through the 8500S through the following blocks:
•
Input Conditioning, including sample rate conversion, defeatable 30 Hz highpass
filtering, and defeatable phase rotation
•
Stereo Enhancement
•
Two-Band Gated AGC, with target-zone window gating and silence gating
•
Equalization, including high-frequency enhancement
•
Multiband Compression with embedded HF clipping and additional HF limiter
•
“Intelligent” Clipping with distortion control, distortion cancellation, and anti-
aliasing
•
Overshoot Compensation
•
DSP-derived Stereo Encoder (generator)
•
Composite Level Control Processor
Input Conditioning: The 8500S operates at a 64 kHz sample rate and power-of-
two multiples thereof (up to 512 kHz in the stereo encoder). This allows user-
selectable bandwidths from 15 to 20 kHz at the HD output.
The 15 kHz lowpass filtering in the analog processing’s peak limiting section has a
stopband that begins at 17 kHz. This provides the necessary
±
2 kHz protection for
RDS/RBDS subcarriers as well generous protection of the 19 kHz pilot tone.
The 8500S’s output spectral control is immaculate, ensuring maximum stereo and
RDS coverage. Because there is very little energy above 16 kHz, the 8500S’s digital