MP3 (MPEG-1 Audio Layer 3), more commonly referred to as MP3, is an audio encoding format.

It uses a lossy compression algorithm that is designed to greatly reduce the amount of data required to represent the audio recording, yet still sound like a faithful reproduction of the original uncompressed audio to most listeners. It was invented by a team of European engineers at Philips, CCETT (Centre commun d'¨¦tudes de t¨¦l¨¦vision et t¨¦l¨¦communications), IRT and Fraunhofer Society, who worked in the framework of the EUREKA 147 DAB digital radio research program, and it became an ISO/IEC standard in 1991.

MP3 is an audio-specific format. The compression removes certain parts of sound that are outside the normal human hearing range so cannot be heard by the listener. It provides a representation of pulse-code modulation ¡ª encoded audio in much less space than straightforward methods, by using psychoacoustic models to discard components less audible to human hearing, and recording the remaining information in an efficient manner. Similar principles are used by JPEG, an image compression format.

MP2 (MPEG-1 Audio Layer 2)

In October 1993, MP2 (MPEG-1 Audio Layer 2) files appeared on the Internet and were often played back using the Xing MPEG Audio Player, and later in a program for Unix by Tobias Bading called MAPlay, which was initially released on February 22, 1994 (MAPlay was also ported to Microsoft Windows).

Initially the only encoder available for MP2 production was the Xing Encoder, accompanied
by the program cdda2wav, a CD ripper used for extracting CD audio tracks to Waveform Audio Files.

The Internet Underground Music Archive (IUMA) is generally recognized as the start of the
on-line music revolution. IUMA was the Internet's first high-fidelity music web site, hosting
thousands of authorized MP2 recordings before MP3 or the web was popularized.

Bit rate

Several bit rates are specified in the MPEG-1 Layer 3 standard: 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256 and 320 kbit/s, and the available sampling frequencies are 32, 44.1 and 48 kHz. A sample rate of 44.1 kHz is almost always used since this is also used for CD audio, the main source used for creating MP3 files. A greater variety of bit rates are used on the internet. 128 kbit/s is the most common since it typically offers very good audio quality in a relatively small space. 192 kbit/s is often used by those who notice artifacts at lower bit rates. By contrast, uncompressed audio as stored on a compact disc has a bit rate of 1378.125 kbit/s (16 bits/sample ¡Á 44100 samples/second ¡Á 2 channels / 1024 bits/kilobit).

Some additional bit rates and sample rates were made available in the MPEG-2 and the MPEG-2.5
standards: bit rates of 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160 kbit/s and sample rates of 8, 11.025, 12, 16, 22.05 and 24 kHz.

Non-standard bit rates up to 640 kbit/s can be achieved with the LAME encoder and the freeformat option, but few MP3 players can play those files. Gabriel Bouvigne, a principal developer of the LAME project, says that the freeformat option is compliant with the standard but, according to the standard, decoders are only required to be able to decode streams up to 320 kbit/s.