Orban OPTIMOD-FM 8700, Operating Manual

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OPTIMOD-FM DIGITAL OPERATION
3-7
About the 8700i’s Signal Processing Features
Dual-Mono Architecture
The 8700i 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 inde-
pendently on the left and right channels—we assumed that the 8700i would always
process stereo program material.
Signal Flow
The signal flows through the 8700i through the following blocks:

Input Conditioning, including sample rate conversion, defeatable 30 Hz highpass
filtering, and defeatable phase rotation

“Multipath Mitigator” phase corrector

Stereo Enhancement

Two-Band Gated AGC, with target-zone window gating and silence gating

Xponential Loudness

Equalization, including high-frequency enhancement and Subharmonic synthe-
sizer

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 8700i 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.