compressor

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(n.) An audio signal-processing device used to reduce the dynamic range of a signal passing through it. The input dynamic range of a 100 dB signal could exit a compressor with a modified dynamic range of 60 dB. This is accomplished by using a voltage-controlled amplifier. The control voltage becomes a function of the input signal’s dynamic content. The need to compress arises when sounds are recorded or broadcast. The sound of a live band may exceed 120 dB in dynamic range, while recording and broadcasting medium have a very limited dynamic range. A cassette tape and an FM broadcast both have a maximum 60 dB of dynamic range. Compressors seem to make loud sounds quieter and quiet sounds louder. Sound engineers set a threshold point below which the program is unaffected, and all audio above the threshold is compressed by the amount determined by a ratio control. In most applications, compressors are used to reduce the dynamic range of only the loudest signals.