Peak Control; High-Frequency Limiting To Reduce - Orban 8182A Operating Manual

sounds louder
than
would
a the
same amount
of sound energy
in
a
narrower
range,
and
3) the
time-constants of the individual
spectral detectors in the
ear
affect the
perceived loudness of a sound,
as
does
4)
the overall duration of the sound.
OPTIMOD-TV's
loudness
controller
is
based
on
a
model
(developed
as a result
of
twenty
years
of
research
at
the
CBS
Technology
Center)
that
analyzes
sound with
reference
to
these psychoacoustic
factors.
When
die
model
indicates that
one
of
these
factors will affect the subjective loudness, the loudness control
enhances
the
main
gain control
signals
with
its
own
control
signal.
The
loudness
controller
reduces loudness gently and
subtly.
Since
it
reduces the
audio drive
to
the peak-limiting section of
OPTIMOD-TV,
loudness reduction
will
therefore
be accompanied by improvements
in
high-frequency response and lowered
peak-limiting-induced
distortion.
Peak
control.
OPTIMOD-TV
controls
peaks using Orban's patented
Hilbert
Transform
Clipper
cir-
cuit.
The
clipping control adjusts the level
of
the audio driving the
clippers,
and
therefore adjusts the peak-to-average
ratio.
The
clipping control determines the
pri-
mary
trade-off
between
consistent
loudness and
distortion.
Turning up the the clipping control drives the clippers harder, reducing
the peak-
to-average
ratio,
and
making
on-air
loudness
more
consistent
Since
the
amount
of
clipping
is
increased, the audible distortion caused
by
clipping
is
increased.
Lower
settings
yield
less
consistent loudness,
but
result in the cleanest
sound and
best high-
frequency response.
In
our
opinion, the best
setting
for the CLIPPING control
is
-1 when
used with slower
release
times (above 3
if
the
switch
is
set to EXP;
above 6
if
the RELEASE
SHAPE
control
is
set to
LIN).
If faster settings
of
the
RELEASE
time control are used, or
if
program
material
is
not always
clean,
use lower
settings
of
the
clipping control
if
even
small
amounts of
audible distortion
cannot be
tolerated.
Ultimately, your
ears
must judge
how much
distortion
is
acceptable.
But
use worst-case
program
material
like live
voice
and piano
to
make
your
final
decision.
The
clipping control can be used
to adjust
your loudness
relative to
other
stations.
Achieving
inter-station consistency usually requires a
conservative clipping control
setting
(between -1 and
-4),
which
will also give
the cleanest
sound and
best high-
frequency
response.
If
the
RELEASE
time
control
is at
a faster setting
than recom-
mended,
it
may
be necessary
to set
the clipping control
below
-1
to
avoid audible
distortion.
High-frequency
limiting
to
reduce
distortion.
The
H-F limiting control
determines
how
the
processor
avoids high-frequency over-
loads
due
to the
pre-emphasis
curve.
When
set
toward
SOFT, the highs are controlled
mostly
by
limiting
(a
form
of
dynamic
filtering),
which
tends
to
soften highs.
When
set
toward HARD,
the
highs
are
controlled
mostly
by
clipping,
which
could potentially
distort highs.
5-10