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Kevin Rector (talk | contribs) m Disambiguating "transmission" |
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''Note: This article is about audio level compression, which reduces the dynamic range of audio signals. This should not be confused with [[audio data compression]], which reduces the data rate of digital audio signals.''
The term "audio compression", meaning '''audio level compression''' is used in the [[sound recording]] and live [[sound reinforcement]] fields. In this context, it refers to a process whereby the [[dynamic range]] of an audio signal is reduced.
An audio level compressor reduces the dynamic range of an audio signal by using a variable gain amplifier to reduce the gain of the signal if it passes a set threshold. The amount of gain reduction is usually determined by a ratio control. That is, with a ratio of 4:1, if the input level is 4[[decibel|dB]] over the threshold, the gain will be reduced so that the output level will only be 1dB over the threshold.
Compressors usually have controls to set how fast the compressor respondes to changes in input level, known as ''attack'', and how quickly the compressor returns to no gain reduction once the input level is below the threshold, known as ''release''. Also, because the compressor is reducing the gain (or level) of the signal, the ability to add a fixed amount of gain at the output is provided so that an optimum level can be used.
In [[telecommunication]], this operation and its reverse are together known as '''companding''' (for '''comp'''ressing and ex'''panding''') so called because the [[dynamic range]] of signals is compressed before [[transmission (telecommunications)|transmission]] and is expanded to the original value at the receiver.
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