Orban OPTIMOD-FM 8600Si, Operating Manual

Page: 29 / 356

OPTIMOD-FM DIGITAL INTRODUCTION
1-3
Absolute Control of Peak Modulation
•
The 8600Si provides universal transmitter protection and audio processing
for FM broadcast. It can be configured to interface ideally with any commonly
found transmission system in the world, analog or digital.
•
The 8600Si provides pre-emphasis limiting for the internationally used pre-
emphasis curves of 50
μ
s and 75
μ
s. Compared to its predecessor, its new clip-
ping/preemphasis-control technology preserves 2.5 to 3 dB more high frequency
energy while significantly reducing audible clipping distortion at all frequencies.
This produces a clean, open sound whose subjective brightness more closely
matches the original program.
•
The 8600Si achieves extremely tight peak control at all its outputs—analog,
AES3 (for both the analog FM and HD channels), and composite baseband.
•
The stereo encoder has two outputs with independent level controls, each ca-
pable of driving 7
5Ω
in parallel with 47,000pF, (100ft / 30m of coaxial cable).
•
By integrating the stereo encoder with the audio processing, the 8600Si elimi-
nates the overshoot problems that waste valuable modulation in traditional ex-
ternal encoders.
•
The 8600Si prevents aliasing distortion in subsequent stereo encoders or trans-
mission links by providing
bandwidth limiting and overshoot compensated
15 kHz low-pass filters ahead of the 8600Si’s audio outputs and stereo encoder.
•
The 8600Si has an internal, DSP-based stereo encoder (with a patented
“half-cosine interpolation” composite limiter operating at 512 kHz sample
rate) to generate the pilot tone stereo baseband signal and control its peak lev-
el. The composite limiter is a unique, “you can only do this in DSP” process that
beats composite clippers by
preserving stereo imaging while fully protect-
ing the stereo pilot tone, RDS/RBDS, and subcarriers .
•
The stereo encoder’s stereo subchannel modulator can operate in normal double
sideband mode and in an experimental
compatible single sideband mode
that is offered to enable users to compare and assess the two modes. See SSB
Stereo Encoder Operation on page 3-11.
•
The Digital Radio and analog radio processing chains offer ITU-R BS.1770-3+
Loudness Meters and Safety Limiters for use in countries that enforce a
BS.1770 loudness limit on digital and/or analog radio broadcasts.
•
The 8600Si implements “true peak” control in its HD processing chain by
oversampling the HD peak limiter’s sidechain at 256 kHz. This allows the 8600 to
prevent clipping in a playback device’s analog signal path by predicting
and controlling the analog peak level following the playback device’s recon-
struction filter to an accuracy of better than 0.5 dB. For typical program mate-