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JBUUREI
MODEL
7110
Compressors and
Limiters
are
typically
used
in
applications
where
the
dynamic
range
of
the
program
material
is:
1.
Too
large
to
be processed by
the
succeeding equipment.
2.
Too
large
to
be
aesthetically pleasing.
3.
Required
to
be reduced
to
achieve
some
other
artistic
goal.
3.
Where
the
peak-to-peak amplitude
is
too great
for
the
headroom
of
the
following
equipment.
4.
Where
the
average
level
is
too great
for
succeeding equipment;
e.g.
loudspeakers.
The
two
different
names
Limiter
and Compressor
generally
refer to
the
degree
to
which
the
dynamic
range
is
restricted.
The
relationship of
change
of input level to
output
level
is
called
the
compression
ratio
.
If,
for
example an
increase
of
8
dB
input signal
level
should
cause
the
output
to
increase
by
only
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
Compressors,
while
those
with
ratios
higher than
8:1
are
called
Limiters.
By
the
definition just
given the
7110
may
be
considered
a compressor
or
a
limiter
depending on
the
position of
the
ratio
control.
This
manual
will
generally
use
the
phrase compression
to
mean
either
compression
or
iimiting.
The
transfer characteristic
shown
in
Figure
3
indicates the difference
between a
low
compression
ratio
and a
high
compression
ratio.
As
the
input signal
increases from the
bottom
left
corner
of
the
graph
along the
straight
line
A
indicating unity gain,
it
reaches
a
point
called
the threshold
point.
Up
until
that
time the
compressor has had no
effect
on
the
signal
level.
After
the
signal
level
reaches
the threshold, the
compressor reduces
its
gain according
to
the
amount
by which the
input signal
exceeds
threshold,
and
the
setting of
the
ratio
control.
As
you can see from
the
two curves
the low
ratio
control
setting,
shown
as curve
B,
gives
a
much
more
gentie
change
to
the output
level
than
does
the higher
ratio
setting
shown
by
curve
C.
The
Threshold
control
adjusts the
point at
which compression
starts to
happen.
In
many
cases,
much
of
the
program
material
is
below
the threshold
level
and
is
not affected
by
the action
of
the
compressor.
dB
Input
Level
Figure
3
Page 10
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