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PARTI:
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
OPTIMOD-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.
1-1
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