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SECTION
III
OPERATING INSTRUCTIONS
3.1
GENERAL DEFINITIONS
Before operating the 1178 Peak Limiter with program material,
it
may be helpful to become familiar with the terminology used in
this manual
.
Compressors
and
Limit
ers
are typically used in applications
where
the dynamic range of
program material
is
too large to be
processed by succeeding equipment,
or
where
the peak— to— peak
amplitude
is
too large
for
the
headroom
of the following equipment.
The two different names generally refer
to
the
degree
to
which
the dynamic range
is
restricted.
The relationship of input level
change versus output level change
is
called the Compression Ratio
.
If,
for example, an
increase
of
8
dB input signal level should cause
the output to increase
by
2
dB,
this would represent
a
4:1
compression
ratio.
Although
no
strict standards
exist, amplifiers
with compression
ratios of up to 8:1 are typically considered to be Compressors
,
while those with ratios higher than
8:1 are called Limiters
.
By
this definition, the following graph shows that the Model 1178 can
function
as a
compressor
or
a
limiter since
it
has
compression
ratios selectable from 4:1 to 20:1.
FIGURE
3-1.
MODEL 1178 TRANSFER CHARACTERISTICS.
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10
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