MP2 (sometimes incorrectly named Musicam) is a short form of MPEG-1 Audio Layer II, and it is also used as a file extension for files containing audio data of this type. While it has largely been superseded by MP3 for PC and Internet applications, it remains a dominant standard for audio broadcasting as part of the DAB digital radio and DVB digital television standards. It is also used internally within the radio industry, for example in NPR's PRSS Content Depot programming distribution system. MPEG-1 is the designation for a group of audio and video coding standards agreed upon by MPEG (Moving Pictures Experts Group). ... A filename extension or filename suffix is an extra set of (usually) alphanumeric characters that is appended to the end of a filename to allow computer users (as well as various pieces of software on the computer system) to quickly determine the type of data stored in the file. ... MP3 is a popular digital audio encoding and lossy compression format invented and standardized in 1991 by a team of engineers working in the framework of the ISO/IEC MPEG audio committee under the chairmanship of Professor Hans Musmann (University of Hannover - Germany). ... The tower of a personal computer. ... This article is in need of attention. ... This article needs to be cleaned up to conform to a higher standard of quality. ... DVB, short for Digital Video Broadcasting, is a suite of internationally accepted, open standards for digital television maintained by the DVB Project, an industry consortium with more than 300 members, and published by a Joint Technical Committee (JTC) of European Telecommunications Standards Institute (ETSI), European Committee for Electrotechnical Standardization (CENELEC... Digital television (DTV) uses digital modulation and compression to broadcast video, audio and data signals to television sets. ... NPR logo For other meanings of NPR see NPR (disambiguation) National Public Radio (NPR) is a private, not-for-profit corporation that sells programming to member radio stations; together they are a loosely organized public radio network in the United States. ...

For details and a short historic introduction to MP2, see MP3. MP3 is a popular digital audio encoding and lossy compression format invented and standardized in 1991 by a team of engineers working in the framework of the ISO/IEC MPEG audio committee under the chairmanship of Professor Hans Musmann (University of Hannover - Germany). ...

How the MP2 Codec works

MP2 is a sub-band audio encoder, which means that compression takes place in the time-domain. By comparison, MP3 is a transform audio encoder, which means that compression takes place in the frequency-domain after transformation from the time-domain. Also, the MP2 encoder does not exploit interchannel redundancies.

This makes MP2 less efficent than MP3 on low bitrates (lower than 256 kbit/s). In example, a 128 kbit/s MP3 encoded audio usually sounds better than the same audio encoded in 192 kbit/s MP2. Nevertheless, MP2 performs better than MP3 on high bitrates (256 to 384 kbit/s).

Like MP3, MP2 is a perceptual codec which means that it removes information that the human auditory system will not be able to perceive. To choose which information to remove, the audio signal is analyzed by a psychoacoustic model, which models the human auditory system. Research into psychoacoustics has shown that if there is a strong signal on a certain frequency, then weaker signals at frequencies close to the strong signal's frequency cannot be perceived by the human auditory system. This is called frequency masking. Perceptual audio codecs take advantage of this frequency masking by not transmitting information at frequencies that are deemed to be imperceptible.

MP2 splits the input audio signal into 32 sub-bands and if the audio in a sub-band is deemed to be imperceptible then that sub-band is not transmitted. MP3, on the other hand, transforms the input audio signal to the frequency domain resulting in 576 frequency components. Therefore, MP3 has a far higher frequency resolution than MP2, which allows the psychoacoustic model to be applied more accurately than for MP2. Because the psychoacoustic model can be applied more accurately, MP3 has greater scope to reduce the bit rate, which is why MP3 requires a lower bit rate than MP2 to get an acceptable audio quality.

Musepack is an MP2-based encoder with several improvements which make it perform better on lower bitrates. Musepack or MPC is an open source lossy audio codec, specifically optimized for transparent compression of stereo audio at bitrates of 160-180 kbit/s. ...

Use in DVD-Video

All DVD-Video players in PAL countries contain stereo MP2 decoders, making MP2 a possible competitor to Dolby Digital in these markets. While some DVD recorders record in MP2 and many consumer-authored DVDs use the format, as of 2005 mass produced discs with MP2 soundtracks are very rare. DVD is an optical disc storage media format that is used for playback of movies with high video and sound quality and for storing data. ... For other meanings of PAL see PAL (disambiguation). ... Dolby Digital is the trademarked marketing name for Dolby Laboratories lossy AC-3 codec. ... A DVD recorder is a consumer electronics device that records analog or digital audio/visual (A/V) signals in a digital format onto a digital video disc (DVD). ... 2005 is a common year starting on Saturday of the Gregorian calendar. ...

Naming confusion

The term and file extension MP2 usually refer to data in the MPEG-1 Audio Layer II format, but can also refer to MPEG-2 BC Audio Layer II, a backwards compatible extension which adds support for multi-channel sound and lower sampling rates. MP2 should not be confused with MPEG-2 video or MPEG-2 AAC audio formats. Multichannel audio refers to the use of multiple sound sources to create a richer, or live music experience. ... MPEG-2 (1994) is the designation for a group of coding standards for digital audio and video, agreed upon by MPEG (Moving Pictures Experts Group), and published as the ISO/IEC 13818 international standard. ... Advanced Audio Coding (AAC) is a lossy data compression scheme intended for audio streams. ...

External links

• MPEG Audio FAQ
• MPEG Audio Resources and Software
• TooLAME - an MP2 encoder
• TwoLAME - a fork of the tooLAME code