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JBUUREI
MODEL
7110
The
compression
ratio
is
generally
understood
to
be
constant.
That
is,
no
matter
how much
gain reduction
is
taking place, the
ratio
of input
change
to
output
change
is
the
same.
This
results
in
a
straight
line
from
the threshold
point.
As
you can see
from the curves
in
Figure
4,
the
initial
compression
ratio
of
the
71
10
is
not
linear.
Rather
it
starts at
a
very low value
and
gradually increases
to
the
setting of
the
front
panel
ratio
control.
This
smooth
"knee"
has
been a
feature
of
UREI
limiters
from
the
days
of
the
famous
LA2A
and
is
a
major reason
for
their popularity.
It
reduces
the
initial
effect of
limiting
action
and
makes
the
limiter
less
obtrusive
in
its
action.
We
use
the
term
Smart-Slope™
to refer to this characteristic
in
the
71
1
0.
The
two curves
show
the
different effect
on
low
ratio
and
high
ratio
settings.
Figure
4
The
attack
time
of
the
Model
71
1
0
is
the time
it
takes
for
the
unit to
respond
to
a
signal vyhich
exceeds
threshold.
The
average responding
section
of
the
7110 has a
variable attack time
of
1
to
50
milliseconds.
The peak
responding
section
has a
fixed
attack
time
of
less
than
100
microseconds.
The
release time
is
the time
which
it
takes
for
the
compressor
to return to
its
normal
gain
after
the
signal
which has
caused compression has
fallen
below
the threshold
levej.
The
release
time
of
the
average
responding
section
of
the
7110
is
also variable
from
50
milliseconds
to
2
seconds
for
1
0
dB
of
release.
As
noted above, the
7110
actually
consists
of
two compressors
in
the
same
package-one
with
an average responding
detector,
and one
with
a peak
responding
detector.
The
difference
between
the
two
detectors
is
their
time constant-that
is,
the length
of
time
that
signal
must exceed
the threshold
level
before
limiting
action
is
initiated,
and
the
speed
with
which
the
limiting
action
is
removed
as
the
signal
is
reduced
in
amplitude.
There
are
good
reasons
for
each,
and
we
will
discuss several
of
them
now. But
first
we
need
to
understand
the difference
between
the
average
signal
level
and
the
peak
signal
level
in
program
material.
The
average
level
is
just
that-the
average.
Taken
over
some
period
of
time,
including
periods
of
silence
(if
any),
periods
of
very high amplitude
signal,
and
periods
where
the
signal
level
is
somewhere
in-between.
The peak
level
is
the
maximum
level
that
a
signal
achieves, again
measured
during
some
time
period.
It
is
important
to realize that
in
audio
program
material that the
ear
responds
roughly
to
the
average
signal
level,
while the electronics
may
have
limitations
that
are
based on
the
peak
signal
level.
Different
types
of
audio
program
material,
from
different
sources,
have
different
peak-to-average
ratios.
From
the
flute,
which produces almost sine-wave pure tones
with
a
Page
11
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