Orban 8300J Operating Manual Download

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OPTIMOD-FM DIGITAL

INTRODUCTION

1-11

processor and the stereo encoder. We therefore recommend using the 8300 with its
built-in stereo encoder whenever practical.

Best Location for OPTIMOD-FM

The best location for OPTIMOD-FM is as close as possible to the transmitter, so that
its stereo encoder output can be connected to the transmitter through a circuit path
that introduces the least possible change in the shape of OPTIMOD-FM’s carefully
peak-limited waveform — a short length of coaxial cable. If this is impossible, the
next best arrangement is to feed the 8300’s AES3 digital output through an all-
digital, uncompressed path to the transmitter's exciter.

Use the 8300’s left and right analog audio outputs in situations where the stereo en-
coder and exciter are under the jurisdiction of an independent transmission author-
ity, and where the programming agency’s jurisdiction ends at the interface between
the audio facility and the link connecting the audio facility to the transmitter. (The
link might be telephone / post lines, analog microwave radio, or various types of
digital paths.) This situation is not ideal because artifacts that cannot be controlled
by the audio processor can be introduced by the link to the transmitter, by transmit-
ter peak limiters, or by the external stereo encoder.

If the transmitter is not accessible:

All audio processing must be done at the studio and you must tolerate any damage
that occurs later. If you can obtain a broadband (0-75 kHz) phase-linear link to the
transmitter, and the transmitter authority will accept the delivery of a baseband en-
coded signal, use the 8300’s internal stereo encoder at the studio location to feed
the STL. Then feed the output of the STL receiver directly into the transmitter’s ex-
citer with no intervening processing.

If an uncompressed AES3 digital link is available to the transmitter, this is also an ex-
cellent means of transmission, although it will not pass the effects of the 8300’s
composite processor (if you are using it). However, if the digital link employs lossy
compression, it will disturb peak levels.

If only an audio link is available, use the 8300’s left and right audio outputs and feed
the audio, without pre-emphasis, directly into the link. If possible, request that any
transmitter protection limiters be adjusted for minimum possible action —
OPTIMOD-FM does most of that work. Transmitter protection limiters should re-
spond only to signals caused by faults or by spurious peaks introduced by imperfec-
tions in the link. To ensure maximum quality, all equipment in the signal path after
the studio should be carefully aligned and qualified to meet the appropriate stan-
dards for bandwidth, distortion, group delay and gain stability, and such equipment
should be re-qualified at reasonable intervals. (See

Optimal Control of Peak Modula-

tion Levels

on page 1-10).

If the transmitter is accessible:

You can achieve the most accurate control of modulation peaks by locating
OPTIMOD-FM at the transmitter site and then using its stereo encoder to drive the
transmitter. You can usually also obtain good results by locating OPTIMOD-FM at the

Orban 8300J, Operating Manual

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