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3.0 A DISCUSSION OF GAIN REDUCTION
There
are
several
misunderstandings
about
limiting and
compression among audio professionals.
Compression and limiting
are sometimes referred to interchangeably, for example.
To
clearly
understand
the
operation
of
the
studio
Dominator, it is
good to have
a standard definition
of terms,
and
have
a
clear
understanding
of
the
differences between
leveling, compression, limiting, and clipping.
Therefore,
this
section will discuss
the terminology, offer
what we think
are
the
most
accurate
definitions,
and
describe
the
basic
principles.
3.1
Leveling
"Leveling", or AGC, is control of long-term average levels.
The ratio is fairly high
(>10:1),
with slow attack and
release
times,
and
a low
threshold.
Because
of the
slow operation,
leveling
has
little
or
no effect
on
short-term
changes in
average level or on transients.
3.2 Compression and Limiting
"Compression" is a popular contraction of the general
term
"dynamic range compression", where
"dynamic
range" refers to the
difference
between
the minimum
signal
level and
the maximum
signal
level
from
an
audio
source over
a
period
of time.
Limiting may be defined as
a subset of compression because
the
dynamic
range
is reduced
through limiting.
However, because
there
are
significant
differences
between
what
are
called
"lim1 ters"
and
11
compressors" ,
it
is
best
not
to
equa te
compression and limiting in application oriented thinking.
Compressors are
used principally
where it
is desired
to
force an audio signal to
maintain a more constant power
level.
This may be to improve the signal-to-noise ratio in a system, to
correct excessively varying volume levels from a program source,
or
for
effects like
gathering greater
loudness.
One
way to
think of
this is
that compression
tries to
keep levels
from
falling too
low.
Limiting,
in contrast,
is used
where it is
required that a signal
be stopped from exceeding
some specific
level.
These applications include prevention of overmodulation,
speaker
protection,
overcutting
protection,
system
overload
protection.
transient
peak
elimination,
etc.
.For
certain
applications
it
is necessary
to
combine a
compressor
and a
limiter to get the desired results.
This might be where we
are
required to maintain a high average signal level constantly near
7
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