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Dynamics processors alter
the dynamics of an audio signal. The most common
types are compressors/expanders, limiters, and
gates/mutes.
Some terms
that may be useful to know
include:
- Dynamic
range: the difference between
the quietest and loudest
components of an audio signal,
from noise floor to distortion;
usually measured in decibels
(dB).
- Peak:
refers to the highest amplitude
and volume of an audio signal.
Common
Uses of Dynamics Processors
Dynamics
processors can be used to change
what you notice in an audio
track; for example, a compressor
might be used to enhance the
breathiness of a vocal track
by making the quiet details
in the recording proportionately
louder.
Dynamics
processors are also useful
in removing or de-emphasizing
unwanted parts of an audio
signal. A gate/mute is often
used to cut out unwanted types
of sound completely, as in
stopping signal flow during
the pauses between snare hits
on a drum track. A de-esser
is essentially a compressor
with sidechain EQ that de-emphasizes
the sibilant quality of an
audio signal, such as harsh
vocal consonants. An expander
increases dynamic range, and
is commonly used in noise reduction
processes: the noise floor,
the quietest part of the audio
signal, is expanded then removed.
Dynamics
processors are frequently applied
as tools for preventing an
audio signal from being overdriven
and causing distortion. A limiter
can be used to prevent the
loudest peaks in an audio signal
from reaching an undesirable
level.
Types of
Dynamics Processors
Compressors
A compressor
decreases the amplitude of
the loudest components of an
audio signal, thus decreasing
the entire dynamic range. Gain
control enables the user to
boost the compressed signal
so that the re-proportioned
audio signal gets louder overall.
This is sometimes called "make-up
gain", because it allows the
user to "make up" the difference
between the original signal
peak level and the compressed
signal peak level. Now the
originally quiet parts of the
audio signal are much louder,
and the loud parts remain loud.
Engineers
refer to extremely compressed
audio as "squashed", meaning
that the balance between quiet
and loud has been destroyed;
sometimes this is a desired
effect, though more often it
creates an exaggerated, unnatural
sound.
How
do I use a compressor?
Understanding
the basic controls on a compressor
is the best way to get started;
then you can experiment until
you get the sound you want.
Compressors typically have
four basic functions: compression
ratio, attack, release, and
gain control.
The compression
ratio expresses the difference
between the input level change
and the output level change.
A compression ratio of 6:1,
for example, indicates that
for every 6dB of level change
on the input signal there is
only 1dB of level change on
the compressed signal. The
higher the compression ratio,
the smaller the dynamic range.
The attack
setting on a compressor determines
how fast it will react to the
input sound. Short attack times
quickly bring down the level
of the loud, fast transients
in the audio signal; long attack
times let more sound through
before the compressor engages,
resulting in a punchier sound.
The release
setting on a compressor determines
how quickly the signal level
returns to its original level
after the compressor has engaged.
Short release times create
a more exaggerated effect ("breathing"),
whereas long release times
have a more gradual, natural
sound.
Gain
control on a compressor typically
allows the user to adjust the
overall volume of the audio
signal; often there are both
input and output level controls
so that you can affect the
initial compression level partially
by input control, and boost
the compressed signal to "make
up" the difference between
the original and compressed
peak level. A sidechain in
a compressor controls the actual
gain element of the compressor.
Most compressors have sidechain
inputs which allow you to change
the signal being fed to the
gain control element. This
can be useful for studio tricks
such as feeding gates or EQ
(for de-essing) to the compressor.
1
. . . 2 . . . 3 Compression:
How to get started using a
compressor
- Set
the gain control/makeup somewhere
below 0dB (and be prepared
to move either way with it,
depending on your output
volume)
- Set
the compression ratio to
something moderate (eg: 4:1 — 8:1)
- Set
a moderately short attack
and moderately long release
time (go halfway on each
control for starters)
Now send
audio though the compressor
and start experimenting with
changing the controls!
Limiters
A limiter
sets a limit on the level of
an audio signal, and typically
compresses only the highest
peaks. There are several basic
types of limiters. Look-ahead
limiters gauge the potential
of the signal to exceed a certain
limit and engage as soon as
they anticipate loud passages.
Brick wall limiters are less
dynamic and engage at precise
set levels. Limiting amplifiers/maximizers
maximize the potential of the
audio signal, by preventing
it from exceeding certain levels
and highly compressing the
dynamic range.
Gates/Mutes
A gate
essentially opens or closes
on an audio signal, silencing
certain parts of the signal.
The threshold setting determines
the signal level at which the
gate will engage. Lower thresholds
allow more sound through the
gate, whereas higher thresholds
cut off more of the sound.
The Wrap-Up
on the Lowdown
If you
have a basic understanding
of how each control on a dynamics
processor affects the audio
signal, it is much easier to
determine what type of sound
will result. Experimenting
with a variety of settings,
changing one control at a time,
will help you understand how
the controls interact. Product
manuals can be extremely useful
resources for learning to use
your dynamics processors, as
every design is slightly different
and some controls interact
in unexpected ways. Many dynamics
processors have presets that
can help get you started.
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