Compression & Encryption: Algorithms & Software by D. James Benton

Author:D. James Benton [Benton, D. James]
Language: eng
Format: epub
Publisher: UNKNOWN
Published: 2019-07-14T22:00:00+00:00

Chapter 14. MP3

The MP3 audio compression and associated file format was developed by Moving Picture Experts Group (MPEG) and initially release in 1993. It was originally designated MPEG-1 (or MPEG–2) Audio Layer III and later shortened. MP3 uses lossy data-compression through approximation as well as discarding parts of the data, which are considered less important or cannot be detected by the human ear. Sound data are subjected to what is called psychoacoustic analysis—an elaborate term referring to the hearing capability and perception of most humans. Typical compression ratios are 75% to 95%, much like that achieved with JPG encoding of photographs.

Sound data on a CD has the form of literal digitized intensities at some specified sampling rate (e.g., 8, 12, 16, 24, 32, or 48 kHz). There may be a single (mono) or two (stereo) data streams. MP3 roughly follows this same categorization, only compressed by transforming the data from the temporal (time) to tonal (frequency) domain. Playback involves the reverse transformation into the time domain While MP3 was only supported by a few software and hardware products in the 1990s, it is now ubiquitous. The Web abounds with free MP3 software, music is readily available, and so are players. Virtually all cellular phones and smart devices recognize the format. A Fast Fourier Transform (FFT) is used to convert the sound data from the time to frequency domain, followed by integer approximation and truncation, as well as filtering. Specific details of the file format and the transformation process will be left to the many web sites devoted to this subject.

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