تويت
Audio Compression: Audio Compression Tutorial
Made Easy By Amr Total
Using a compressor on a microphone or on a
recorded track may seem to be a simple task,
however, there’s a lot to learn about the theory
of compression. Understanding this theory and
why compression is useful will help you in using
these devices more effectively. Compressors are
“dynamic range processors” or “variable gain
amplifiers” (VGA’s). They affect the dynamic
range of sound by varying the “gain” (volume) of
that sound.
If the dynamic range of music is potentially
near 120db (that’s loud!) and the dynamic range
of recording devices and live sound systems are
only near 75-90db, we need a way to control the
dynamic range so that those loud levels do not
cause distortion. The dynamic range has to be
gain reduced to a level appropriate for
recording or a live concert. This "gain
reduction" could be accomplished by manually
riding the fader up and down but our hands are
not fast enough. A compressor automatically
controls the volume of a sound, leaving our
hands free for other things.
Compressors are used on vocals, bass, guitar,
drums and almost anything that fluctuates
widely. Very simply put, a compressor is an
amplifier whose gain decreases as the input
increases. It makes big changes into smaller
changes.
Most compressors have 4 main controls: input
level, output level, threshold and ratio. Some
compressors also have attack time and release
time controls.
Input level: is exactly that, the amount of
input level. When you set it to "O", you get the
exact level that you are sending from your mic
pre-amp or from an already recorded track.
Output level: the amount of output after
compression.
Threshold: A set point at which the compressor
begins to work. Incoming levels below your set
threshold are unprocessed. Incoming levels above
your set threshold are compressed according to
the compression ratio. The threshold on a
compressor is similar to an air conditioner
thermostat. When the temperature exceeds a
certain threshold, the air conditioner kicks in.
When the temperature drops below threshold, the
air conditioner shuts off. This is the same idea
for the threshold of a compressor.
Ratio: is the ratio of the input signal to the
output signal after compression.
Example: 4:1 ratio means if the input is 12db,
the output level is only 3db. So level input
(12db) divided by ratio (4) is the output level.
A ratio of 2:1 would give a 12 db input an
output level of 6 db and a ratio of 8:1 would
give an output level of 1.5db. So the rule of
thumb is, the higher the ratio, the more extreme
the compression is going to be. Therefore,
ratios from 2:1 up through 6:1 are considered
“gentle” and ratios above 6:1 are considered
“hard”. “Hard” compressing is called “limiting”.
A limiter is merely a compressor with a very
high ratio, very fast attack times, fast to
medium release times and high thresholds.
Limiters are great for live sound systems as a
safety device when very high levels are
introduced into the system. Any signal above the
threshold is "clipped" off. They protect
speakers from blowing. 8:1,10:1, 20:1, 100:1 are
common limiting ratios.
Attack time: The speed with which the device
affects the signal. The time it takes to react
to a signal above the threshold.
Release time: The rate at which the device lets
the signal decay. The time the compressor takes
to return the signal to normal (the way it was
before hitting the threshold).
Stereo compressors come in one box with 2
channels and can be used in 2 different ways.
You can put 2 individual mics or tracks into it
and each channel will have completely
independent settings from each other. Obviously,
a mono compressor just has one channel. The
second way to use a stereo compressor is to put
an entire stereo studio mix or the stereo output
of a live soundboard into it. This is called
using the compressor as a Left/Right Stereo Bus
compressor. When you use it as a L/R Stereo Bus
compressor, you have to link both sides
electronically so the same amount of compression
happens on both sides at the same time.
A “Frequency Selective Compressor “(De-esser) is
a special compressor that reduces the level of a
very narrow band of frequencies. It’s very
useful when a singer has a strong, sharp,
sibilant “S” to their voice. Typically in the
5-8k range. When 5-8k exceeds the threshold, it
reduces strong, sibilant "S's" without affecting
the rest of the word.
There are 2 types of compressors: Tube and solid
state. They have a wide range of quality and
price ($200-$4000). Upper mid price and
expensive compressors can compress a signal
heavily and you can hardly tell it's working.
The sound remains much more natural than when an
inexpensive compressor is compressing.
Tube compressors have such a great sound that
sometimes a signal is put through it just to get
the sound of the tubes while hardly compressing
it at all.
Be careful not to overuse a compressor. When
overused, it creates a very unnatural sound. The
trick is to learn to use a compressor in a
subtle manner.
Made Easy By Amr Total
Using a compressor on a microphone or on a
recorded track may seem to be a simple task,
however, there’s a lot to learn about the theory
of compression. Understanding this theory and
why compression is useful will help you in using
these devices more effectively. Compressors are
“dynamic range processors” or “variable gain
amplifiers” (VGA’s). They affect the dynamic
range of sound by varying the “gain” (volume) of
that sound.
If the dynamic range of music is potentially
near 120db (that’s loud!) and the dynamic range
of recording devices and live sound systems are
only near 75-90db, we need a way to control the
dynamic range so that those loud levels do not
cause distortion. The dynamic range has to be
gain reduced to a level appropriate for
recording or a live concert. This "gain
reduction" could be accomplished by manually
riding the fader up and down but our hands are
not fast enough. A compressor automatically
controls the volume of a sound, leaving our
hands free for other things.
Compressors are used on vocals, bass, guitar,
drums and almost anything that fluctuates
widely. Very simply put, a compressor is an
amplifier whose gain decreases as the input
increases. It makes big changes into smaller
changes.
Most compressors have 4 main controls: input
level, output level, threshold and ratio. Some
compressors also have attack time and release
time controls.
Input level: is exactly that, the amount of
input level. When you set it to "O", you get the
exact level that you are sending from your mic
pre-amp or from an already recorded track.
Output level: the amount of output after
compression.
Threshold: A set point at which the compressor
begins to work. Incoming levels below your set
threshold are unprocessed. Incoming levels above
your set threshold are compressed according to
the compression ratio. The threshold on a
compressor is similar to an air conditioner
thermostat. When the temperature exceeds a
certain threshold, the air conditioner kicks in.
When the temperature drops below threshold, the
air conditioner shuts off. This is the same idea
for the threshold of a compressor.
Ratio: is the ratio of the input signal to the
output signal after compression.
Example: 4:1 ratio means if the input is 12db,
the output level is only 3db. So level input
(12db) divided by ratio (4) is the output level.
A ratio of 2:1 would give a 12 db input an
output level of 6 db and a ratio of 8:1 would
give an output level of 1.5db. So the rule of
thumb is, the higher the ratio, the more extreme
the compression is going to be. Therefore,
ratios from 2:1 up through 6:1 are considered
“gentle” and ratios above 6:1 are considered
“hard”. “Hard” compressing is called “limiting”.
A limiter is merely a compressor with a very
high ratio, very fast attack times, fast to
medium release times and high thresholds.
Limiters are great for live sound systems as a
safety device when very high levels are
introduced into the system. Any signal above the
threshold is "clipped" off. They protect
speakers from blowing. 8:1,10:1, 20:1, 100:1 are
common limiting ratios.
Attack time: The speed with which the device
affects the signal. The time it takes to react
to a signal above the threshold.
Release time: The rate at which the device lets
the signal decay. The time the compressor takes
to return the signal to normal (the way it was
before hitting the threshold).
Stereo compressors come in one box with 2
channels and can be used in 2 different ways.
You can put 2 individual mics or tracks into it
and each channel will have completely
independent settings from each other. Obviously,
a mono compressor just has one channel. The
second way to use a stereo compressor is to put
an entire stereo studio mix or the stereo output
of a live soundboard into it. This is called
using the compressor as a Left/Right Stereo Bus
compressor. When you use it as a L/R Stereo Bus
compressor, you have to link both sides
electronically so the same amount of compression
happens on both sides at the same time.
A “Frequency Selective Compressor “(De-esser) is
a special compressor that reduces the level of a
very narrow band of frequencies. It’s very
useful when a singer has a strong, sharp,
sibilant “S” to their voice. Typically in the
5-8k range. When 5-8k exceeds the threshold, it
reduces strong, sibilant "S's" without affecting
the rest of the word.
There are 2 types of compressors: Tube and solid
state. They have a wide range of quality and
price ($200-$4000). Upper mid price and
expensive compressors can compress a signal
heavily and you can hardly tell it's working.
The sound remains much more natural than when an
inexpensive compressor is compressing.
Tube compressors have such a great sound that
sometimes a signal is put through it just to get
the sound of the tubes while hardly compressing
it at all.
Be careful not to overuse a compressor. When
overused, it creates a very unnatural sound. The
trick is to learn to use a compressor in a
subtle manner.
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