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23
USING COMPRESSION - INTRODUCTION
Compression in general
If you are an experienced user of audio Compressors you
may want to skip this section, which is a general
explanation of what Compressors do and how they are
applied in audio production.
Compression is generally used to reduce the dynamic
content of an audio signal. Now, why is this necessary?
Compared to the human ear any electronic reproduction of
audio is limited by the available technology. Whereas the
human ear has an incredible flexibility/dynamic range, let-
ting you hear a pin dropping one moment, and an airplane
taking off the moment after, - various physical limitations of
the electronic components makes this type of flexibility
impossible to achieve in audio reproduction.
Electronic reproduction of sound has two limitations. In the
low end, the signal level must be well above the base
noise, also referred to as the “noisefloor” introduced by the
electronic components. The upper limit is determined by
the internal operating voltages. If exceeded, distortion will
be the result. As a certain amount of headroom needs to
be reserved for peaks in the audio material even less
dynamic range is available. So, on one hand you would like
to have as much headroom as possible, but at the same
time avoid having the average level too close to the noise
floor. This is where compression is applied. With the
Compressor you control/reduce the peaks in the audio
signal and the average level of the audio signal can be
increased.
The first type of Compressors (in the 1930's) were very
simple constructions with two controllable parameters. With
one of the two controls the user had to find a setting based
upon an presumed average audio level of the material
about to be processed. The other control (Ratio) specified
the reduction of dynamic content in the entire signal that
passed through the unit. This way the signal was com-
pressed from both sides, low levels were increased by the
same amount as the high levels were decreased.
Modern Compressors uses a Threshold point. When the
signal increases above the specified Threshold point the
Compressor begins to reduce the Output signal by an
amount set by the Ratio parameter. Once the signal drops
below the Threshold point the Compressor stops interfering.
Compressors vs Limiters
Where the Compressor mostly is is used to gradually
reduce the dynamic content above the set Threshold point
a limiter is used to directly avoid hitting an upper limit.
Compressors and limiters are often used in conjunction. -
The Compressor as the musical/gentle way of reducing the
level and the limiter as a hard abrupt control to avoid
distortion/clipping.
Multi-band Compression
With multi-band Compressors such as the TRIPLE•C you are
able to differentiate the compression on different frequency
areas in the audio signal. The audio signal is split in to
several frequency areas and you can obtain considerably
better results when working with a complex signal with a
wide frequency area. When working with an non-multi-band
Compressor on e.g. a bass drum will invoke the Compressor
to reduce the dynamic content of the entire signal when
activated. This gives what it often referred to as the "pump-
ing/breathing" effect. By splitting up the signal in to e.g. 3
bands; low, mid and high and use different Threshold/Ratio
settings on these bands a much better result can be
achieved.
However, there are times to use multi-band compression
and times to use traditional full-range compression. The
TRIPLE•C gives you both.