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PRESONUS
5
2.1 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