Presonus Audio electronic Smart Compressor - Manual (Page 5)

1 OVERVIEW OVERVIEW
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A Word About Compression . . . .
Punch, apparent loudness, presence just three of many terms used to
describe the effects of compression/ limiting.
Compression and limiting are forms of dynamic range (volume) control.
Audio signals have very wide peak to average signal level ratios
(sometimes referred to as dynamic range which is the difference between
the loudest level and the softest level). The peak signal can cause overload
in the audio recording or reproduction chain resulting in signal distortion.
A compressor/limiter is a type of amplifier in which gain is dependent on
the signal level passing through it. You can set the maximum level a
compressor/limiter allows to pass through, thereby causing automatic gain
reduction above some predetermined signal level or threshold.
Compression refers basically to the ability to reduce the output level of an
audio signal by a fixed ratio relative to the input. It is useful for lowering
the dynamic range of an instrument or vocal, making it easier to record
without distorting the recorder. It also assists in the mixing process by
reducing the amount of level changes needed for a particular instrument.
Take, for example, a vocalist who moves around in front of the
microphone while performing, thus making the output level vary up and
down unnaturally. A compressor can be applied to the signal to help
correct this recording problem by reducing the ‘louder’ passages enough
to be compatible with the overall performance.
How severely the compressor reduces the signal is determined by the
compression ratio and compression threshold. A ratio of 2:1 or less is
considered mild compression, reducing the output by two for signals
greater than the compression threshold. Ratios above 10:1 are considered
hard limiting. Limiting refers to the point at which the signal is restrained
from going any louder at the output.
The level of input signal at which the output is reduced is determined by
the compression threshold. As the compression threshold is lowered, more
and more of the input signal is compressed (assuming a nominal input
signal level). Care must be taken not to ‘over compress’ a signal. Too