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PART 1:
Introduction
Function of OPTIMOD-TV: OPTIMOD-TV
is
an integrated signal- processing system
which replaces conventional compressors, limiters, and clippers. It is an adaptation
of the OPTIMO
- FM Model 8100A to TV audio, and offers the TV broadcaster the
same superb
audio quality that has
made the 8100A so popular among FM
radio
broadcasters.
Briefly, the OPTIMOD-TV system performs the following functions:
1.
It rides gain over a range of as much as 25dB, compressing dynamic range and
compensating for gain riding
errors on the part of operators.
The amount of
dynamic range reduction ordinarily produced is adjustable. When OPTIMOD-TV is
operated
at its optimum release time setting, gain riding and compression are
virtually
undetectable
because
of
advanced
program- controlled
time
constants,
level- dependent gating, and multiband compression.
2.
It
controls
excessive
perceived
loudness
by
means
of
a complex
loudness-
estimating
circuit
that
reduces
the
gain
of
the
compressor
VCA's
when
necessary.
The
loudness
controller
circuit
can
be
activated
and
defeated
by
remote
control
or
locally
as
required.
This
circuit
is
licensed
from
CBS
Technology Center and incorporates the results of their second major loudness
research project ( 1978-1980). On- air tests of the controller have indicated that
it
substantially
reduces
or
eliminates
viewer
complaints
regarding
excessively
loud commercials.
3.
It
controls
potential
interference
to
video
and/or
future
stereo
services
by
means
of bandwidth- limiting
15kHz
lowpass filters incorporating
full
overshoot
compensation.
OPTIMOD-TV
thus
provides
extremely
tight
control
over
peak
modulation,
preventing
overmodulation
and
controlling
its
output
spectrum
simultaneously.
4.
The OPTIMOD-TV compressor is a dual- band design which can be operated with
the bands independent of each other (" independent"), or such that the bands are
coupled
and
ordinarily
track
each
other (" wideband").
When
operated
in
"independent"
mode,
OPTIMOD-TV
makes
audio
quality
more
consistent
by
correcting
frequency
balances
between
bass
and
midrange
material.
When
operated
in " wideband"
mode,
it
will
preserve
frequency
balances
and
will
produce an output which sounds like its input.
5.
It
prevents
peak
overload
and
overmodulation
due
to
the
effects
of
the
preemphasis curve.
Each
part
of
the
OPTIMOD-TV
system
has
been
precisely
engineered
to
be
compatible
with
all
other
parts
to
achieve
optimum
performance.
The
basic
OPTIMOD-TV
is
a stereo
unit
with
active
balanced + 10dBm
outputs.
Internal
jumpers determine if the output is to be flat or preemphasized.
In
general,
OPTIMOD-TV
should
be
fed
unprocessed
audio.
However,
additional
compression and/or other audio processing may be desirable if applied to individual
microphone channels in a live production environment, or to other sources requiring
special processing.
OPTIMOD-TV as ordinarily sold
is fully equipped for stereo operation. Little cost
would
be
saved
by
eliminating
components
for
the
second
channel,
and
future
conversion would be somewhat inconvenient. In addition, the second channel provides
a certain measure of redundancy and permits utilization of card-swapping techniques
to diagnose problems.
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