Orban OPTIMOD-FM 8600, Руководство по эксплуатации

Страница: 31 / 397

OPTIMOD-FM DIGITAL INTRODUCTION
1-3
•
The 8600 provides preemphasis limiting for the internationally used
preemphasis 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 8600 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 8600 elimi-
nates the overshoot problems that waste valuable modulation in traditional ex-
ternal encoders.
•
The 8600 prevents aliasing distortion in subsequent stereo encoders or transmis-
sion links by providing
bandwidth limiting and overshoot compensated 15
kHz low-pass filters ahead of the 8600’s audio outputs and stereo encoder.
•
The 8600 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 level. The
composite limiter is a unique, “you can only do this in DSP” process that beats
composite clippers by
preserving stereo imaging while fully protecting 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.
•
Starting with V1.4 software, the 8600HD implements “true peak” control in
the 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 an-
alog signal path by predicting and controlling the analog peak level following
the playback device’s reconstruction filter to an accuracy of better than 0.5 dB.
For typical program material, accuracy is 0.2 dB
Without true peak control, analog clipping can occur even if all peak values of
the digital samples are below 0 dBFS. This phenomenon has also been termed
“
0 dBFS+ .”