1. Audio: The reduction of a span of the greater amplitudes in an audio signal for the purpose of limiting the reproduction of those particular amplitudes with the effect of reducing the difference between peak amplitudes and average amplitudes, making the overall signal sound louder when some gain is added (since peaks will no longer over modulate). 2: Data: A method for reducing the bitrate of a digital representation of an audio signal in order to reduce te storage requirements of the representation. Methods like AAC and MP3 involve the use of psychoacoustic models to discard portions of the audio signal that people will not notice, but always results in artifacts. For professional audio recording, always work with uncompressed audio file formats (e.g. WAV or AIF).