Compression
is a soft effect that can be used to reduce the dynamic range of
an audio signal from an audio segment. When you compress an audio
signal, there is less of a difference between the lowest measured
gain of the signal and the highest measured gain of the signal.
Compression is useful if your audio signal has many different loudness
levels that you want to play back at a similar perceived loudness
level. For example, when recording voice-overs, you may want to maintain
a constant perceived level of loudness in the actor's voice.
You can also compress
an audio signal to attenuate portions of the signal that are too
loud. For example, if your recording is at a consistent loudness
level, but for some reason there is an unwanted peak in loudness
level, you can compress the loud portion to give it the same perceived
loudness as the rest of the recording.
Because compressing an
audio signal could have a drastic effect on the overall dynamic
range of the signal, it is not effective in every situation. For
example, for a complex recording that has been mixed down from many other
audio sources, such as a vocal track with music and sound effects,
the audio signal might have complex differences in loudness levels.
If you compress a master audio signal such as this, you will lose
many of the original qualities of the audio signal. In such cases,
it is advisable that you compress the source audio track before
mixing down.
If you are editing a
pair of mono tracks that you wish to process as stereo tracks, you
should merge both tracks into one stereo audio track. This ensures
that the same compression is used on both left and right channels. See
Creating and Splitting Stereo Audio Tracks.
The Compression soft
effect has the following controls.
| Control |
Values |
Description |
| Threshold |
-60 dB - 0 dB |
Determines the level above which signals are affected by
the compression. Signals below the Threshold are not compressed.
Signals above the Threshold are compressed based on the Ratio setting.
|
| Ratio |
1:1 - 20:1 |
Defines the amount of gain reduction applied to the signal
above the Threshold level. For example, a Ratio of 2:1 means that
for every 2 dB the input signal increases, the output signal will
only increase by 1 dB. Gain reduction is displayed on the compression
meter.
|
| Attack |
0.1 ms - 100 ms |
Defines the speed at which the compression is applied once
the signal has reached the Threshold level. A fast attack rate means
that most of the signal is compressed. A slow attack rate means
the early part of the signal will not be compressed. The result
is more natural sounding than using a fast Attack.
|
| Release |
10 ms - 1000 ms or Auto
|
Defines the speed at which the compressed signal returns
to its original value when the input signal level goes below the
Threshold value. If Auto Release is enabled, the optimal value is
automatically set.
|
| Knee Width |
0 dB - 40 dB |
Defines the bend in the response curve. A low number gives
a sharp angle and a high number gives a wider, rounded edge. A wider
(or softer) knee width reduces the audible change from uncompressed
to compressed. A higher knee width is most effective for higher
ratios where the changeover is more noticeable.
|
| Output Gain |
-10dB - 24 dB |
Defines the amount of gain to add to the output signal. For
example, if you applied a lot of compression to the signal, you
may want to add some output gain to set the output signal to its
original overall loudness level.
|
| Auto Release |
|
When enabled, the optimal Release time is automatically
set according to the input signal.
|
| Peak Detection / RMS Detection |
|
Select Peak Detection to compress the signal based on the
peak levels. Select RMS Detection to compress the signal based on
its average level.
|
