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Dynamic range compression (DRC) or simply compression is an electronic effect unit that reduces the volume of loud sounds or amplifies quiet sounds by narrowing or "compressing" an audio signal's dynamic range. Compression is commonly used in sound recording and reproduction, broadcasting, live sound at music concerts and in some instrument amplifiers (usually bass amps). Audio compression reduces loud sounds which are above a certain threshold while quiet sounds remain unaffected. In the 2000s, compressors are also available in audio software for recording. The dedicated electronic hardware unit or audio software used to apply compression is called a compressor. In recorded and live music, compression parameters may be adjusted by an audio engineer to change the way the effect sounds.Compression and limiting are not different in process but in degree and perceived effect. A limiter is a compressor with a high ratio and, generally, a fast attack time. Limiters are common as a safety device in live sound and broadcast applications to prevent sudden volume peaks from occurring. Limiters are also used as protective features in some components of sound reinforcement systems (e.g., powered mixing boards and power amplifiers) and in some bass amps, to prevent unwanted distortion and/or speaker damage. == Types == Downward compression reduces loud sounds over a certain threshold while quiet sounds remain unaffected. Upward compression increases the loudness of sounds below a threshold while leaving louder passages unchanged. Both downward and upward compression reduce the dynamic range of an audio signal. An expander performs the opposite function, ''increasing'' the dynamic range of the audio signal.〔(Dynamic Range Processing and Digital Effects )〕 Expanders are generally used to make quiet sounds even quieter by reducing the level of an audio signal that falls below a set threshold level. A noise gate is a type of expander.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Dynamic range compression」の詳細全文を読む スポンサード リンク
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