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they are looking
for more "sustain"
for
example.
A
limiter
driven
effectively becomes a compressor.
or a different
to
heavy
gain
"texture!!
J
reduction
Let
us
now
depart
from
further
elaborations
about
compressors,
and
focus
on
two
types
of
1 imi teTS :
tlpeak
1
imi ters" ,
and
"program
1 imi ters" .
At
this
point
i t
is
important to solidify the definition of "peak level".
This term
is taken
to mean
two different
things in
the audio industry.
Sometimes it is used to refer to the highest (or peak) VU
level
occuring in an audio program.
Other times it is used
to refer
to the actual peak amplitude
of the audio wave, which
would be
measured
on
a
peak
program meter
(ppm)
or
an oscilloscope
display, but not on a VU
meter.
Let us define "peak level"
as
the
true
peak waveform
amplitude, and
"peak program"
as the
highest VU level.
3.6.1
Program Limiters
With these definitions in
mind, a "program limiter"
can
be
described
as a
limiter having
all the
previously defined
characteristics
of
a
limiter,
and
whose
detection circuits
result in limiting the "peak program" level (as measured on a VU
meter) to a specified level, usually zero VU, without regard for
the peak level
.
3.6.2
Peak Limiters
A "peak limiter" is used where the absolute audio
waveform
amplitude cannot be allowed to exceed a given value.
Most audio
systems
produce
particularly
objectionable
distortion
when
driven to overload, so peak limiters are often used to
maintain
safe
peak
levels
below
any system
clipping
to
guarantee a
distortion
free
system.
Limiters
in
this
application
are
sometimes
referred
to
as
"protection
limiters".
Another
appl ication
of
peak
1imi ters is
"modulation
limi ting
"
in a
broadcast situation where a
specified peak level is
defined as
100 percent modulation which must not be exceeded.
Peak
limiters
are
usually
characterized
by
fast
attack and release
times, a very
high compression ratio
and a
high
threshold
such that
no
gain reduction
takes
place for
signals whose
peak level
is under
the overload
point of
the
system.
Limiters
wlth
very
fast
release
tend
to generate
distortion under continuous
gain reduction, but
for protection
limiting where limiting
is brief, the
fast action tends
to be
practically
unnoticeable,
maintaining a
clean
sounding audio
system.
10
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