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MP3 compression works by reducing (or approximating) the accuracy of certain components of sound that are considered to be beyond the of most humans. This method is commonly referred to as perceptual coding, or modeling.The remaining audio information is then recorded in a space-efficient manner. Compared to , MP3 compression can commonly achieve a 75 to 95% reduction in size. For example, an MP3 encoded at a constant bitrate of 128 kbit/s would result in a file approximately 9% the size of the original CD audio.
The MP3 lossy algorithm takes advantage of a perceptual limitation of human hearing called . In 1894, the American physicist reported that a tone could be rendered inaudible by another tone of lower frequency. In 1959, Richard Ehmer described a complete set of auditory curves regarding this phenomenon.Ernst Terhardt et al. created an algorithm describing auditory masking with high accuracy. This work added to a variety of reports from authors dating back to Fletcher, and to the work that initially determined critical ratios and critical bandwidths.
