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An
accessory
port
is
included
standard
to
interface
the
unit
with
the
Orban
8182A/SG BTSC Stereo Generator.
Comparison
With
OPTIMOD-FM:
OPTIMOD-TV ( Model
8182A)
is
conceptually
similar to
OPTIMOD-FM ( Model 8100A). If you are
familiar with the 8100A, this
comparison may be of interest. Otherwise, skip to the next section.
The following characteristics are different:
The
stereo
generator ( Card # 7) has been replaced
with a two-channel audio
output
buffer
card
to
drive
an
external
BTSC
television
stereo
generator.
While
the 8182A
can drive any
stereo
generator equipped
with conventional
Left/Right or Sum- And-Difference audio inputs, best results are obtained when
the 8182A is mated with the Orban 8182A/SG BTSC Stereo Generator. This is
because the lowpass filters within the 8182A/SG were specifically designed to
complement
the
lowpass
filters
which
already
exist
within
the
8182A.
In
addition,
the 8182A/SG
interfaces
to
the
8182A
by
means of a special
multipin rear-panel connector, placing the first part of the 8182A/SG lowpass
filtering before the 8182A's preemphasis, high frequency limiter, and Hilbert-
Transform Clipper. This
interleaving of stereo generator and audio processor
circuitry prevents stray 15,734Hz which may be present on the program line
from
spuriously
triggering
the
audio
processor
or
causing
intermodulation
distortion within its peak limiting circuitry.
--
The
output
wiring ( including
the
RF1
filter
card)
has
been
changed
to
accomodate stereo audio.
--
Since the stereo
generator is
omitted,
the STEREO/MONO mode switch and
indicator
lamp
have
been
excluded.
The
rotary
switch
controlling
the
diagnostic VU
meter excludes positions relating
to
the stereo
generator but
has new monitor points for the system outputs.
--
The compressor gating circuitry has been altered to prevent the compressor's
gain from recovering beyond - 10cB in absence of program. This prevents noise
rush-up, especially when the audio source is 16mm optical film.
(The gain of the 8100A was permitted to slowly recover to OcB since source
material used in FM is typically much quieter.)
To avoid operator confusion, three of the four Gain Reduction meters ( Total
Master
G/R, Compressor Master G/R, and Total Bass G/R) have new scales
where 10dB gain reduction is represented as " OcB".
--
Both " linear" and "exponential" compressor release
characteristics have been
made
available. ( The
release
shape
of
the
8100A
is
essentially
linear.)
In " linear" mode,
the compressor releases at a constant number of dB
per
second. In "exponential" mode,
the release starts slowly and speeds up as it
progresses. This
is
useful when
the "open" sound
of slow release
is
desired,
yet large input level changes must be followed quickly.
--
A sophisticated
peak
limiting
circuit
called
the "Hilbert- Transform
Clipper"
has been developed specifically
for TV applications ( where
voice material
is
dominant). This "clipper" replaces the simpler variable-threshold diode clipper
used in the 8100A's distortion-cancelled clipper circuit.
1-2
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