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INTRODUCTION
Designed
primarily
for
use
with
well
controlled
average
input
levels
such
as
provided by Audimax,
the
Model 4300 Volumax unit
supersedes
all
other peak
limiters
in
the
process
of
preventing
carrier
overmodulation.
A.
Conventional
Peak
Limiters
and Instantaneous
Phase
Switches
With conventional
peak
limiters,
the
broadcaster
must
either
reduce
the
program
level
so
much
that
the
limiting
of
peaks
is
not
severe
enough
to
cause
"pumping"
--
thus
lowering
average
modulating power
--
or
must
tolerate
the
"pumping" and consequent
distortion.
Although conventional
limiters
moderate
"pumping" by using long
recovery
times,
the
intervals
im-
mediately following high
program
peaks
waste
modulation capability; in
these
times,
the
limiter
is
insensitive
while
it
recovers
from
reduced
gain.
The
Volumax
unit
may be
regarded
as
an
instantaneous
phase-
switch
limiter.
Limiters
of
this
type may
waste
less
power, but
those
other
than
Volumax
introduce
audible
clicks
whenever
phase
switching occu..-s.
Volumax
is
silent
,
as
shown
in
figure
1-2.
SILENT SWITCHING The two photographs above show the word "content" displayed on an oscilloscope. The
photo on the left taken with the VOLUMAX
in
operation, shows clearly that phase switching took place during
the momentary pause between syllables-completely and silently.
The
photo on the right using an instantaneous
phase switch shows that the phase switching took place during the second syllable-and with an audible click.
Figure
1-2.
Phase
Switching,
Comparison
Waveforms
1-2
