MPEG-1 Audio Layer II
Encyclopedia
MPEG-1 Audio Layer II or MPEG-2 Audio Layer II (MP2, sometimes incorrectly called Musicam or MUSICAM) is a lossy
Lossy data compression
In information technology, "lossy" compression is a data encoding method that compresses data by discarding some of it. The procedure aims to minimize the amount of data that need to be held, handled, and/or transmitted by a computer...

  audio compression format defined by ISO/IEC 11172-3 alongside MPEG-1 Audio Layer I
MPEG-1 Audio Layer I
MPEG-1 Audio Layer I, commonly abbreviated to MP1, is one of three audio formats included in the MPEG-1 standard. While supported by most media players, the codec is considered largely outdated, and replaced by MP2 or MP3....

 and MPEG-1 Audio Layer III (MP3). While MP3 is much more popular for PC
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...

 and Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

 applications, MP2 remains a dominant standard for audio broadcasting.

MUSICAM

MPEG-1 Audio Layer 2 encoding was derived from the MUSICAM (Masking pattern adapted Universal Subband Integrated Coding And Multiplexing) audio codec, developed by Centre commun d'études de télévision et télécommunications
Centre commun d'études de télévision et télécommunications
CCETT or Centre commun d'études de télévision et télécommunications was a research centre created in Rennes in 1972 jointly by the Office de Radiodiffusion Télévision Française and Centre National...

 (CCETT), Philips
Philips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....

, and Institut für Rundfunktechnik
Institut für Rundfunktechnik
The Institut für Rundfunktechnik GmbH is the research centre of the German broadcasters , Austria's broadcaster and the Swiss public broadcaster . It is located in Munich and is responsible for the research and standardisation of broadcasting technology...

 (IRT) in 1989 as part of the EUREKA 147 pan-European inter-governmental research and development initiative for the development of a system for the broadcasting of audio and data to fixed, portable or mobile receivers (established in 1987).

It began as the Digital Audio Broadcast (DAB) project managed by Egon Meier-Engelen of the Deutsche Forschungs- und Versuchsanstalt für Luft- und Raumfahrt (later on called Deutsches Zentrum für Luft- und Raumfahrt, German Aerospace Center) in Germany. The European Community financed this project, commonly known as EU-147, from 1987 to 1994 as a part of the EUREKA
EUREKA
EUREKA, often abbreviated as "E!" or "Σ!", is a pan-European research and development funding and coordination organization. EUREKA aims to coordinate efforts of governments, research institutes and commercial companies concerning innovation...

 research program.

The Eureka 147 System comprised three main elements: MUSICAM Audio Coding (Masking pattern Universal Sub-band Integrated Coding And Multiplexing), Transmission Coding & Multiplexing and COFDM Modulation.

MUSICAM was one of the few codecs able to achieve high audio quality at bit rates in the range of 64 to 192 kb/s per monophonic channel. It has been designed to meet the technical requirements of most applications (in the field of broadcasting, telecommunication and recording on digital storage media) — low delay, low complexity, error robustness, short access units, etc.

The audio coding algorithm used by the Eureka 147 Digital Audio Broadcasting (DAB) system has been subject to the standardization process within the ISO/Moving Pictures Expert Group (MPEG) in 1989–94. MUSICAM audio coding was used as a basis for some coding schemes of MPEG-1 and MPEG-2 Audio. Most key features of MPEG-1 Audio were directly inherited from MUSICAM, including the filter bank, time-domain processing, audio frame sizes, etc. However, improvements were made, and the actual MUSICAM algorithm was not used in the final MPEG-1 Layer II audio standard.

Since the finalisation of MPEG-1 Audio and MPEG-2 Audio (in 1992 and 1994), the original MUSICAM algorithm is not used anymore. The name MUSICAM is often mistakenly used when MPEG Audio Layer II is meant. This can lead to some confusion, because the name MUSICAM is trademarked by different companies in different regions of the world. (Musicam is the name used for MP2 in some specifications for Astra Digital Radio as well as in the BBCs DAB documents.)

The Eureka Project 147 resulted in the publication of European Standard, ETS 300 401 in 1995, for DAB which now has worldwide acceptance. The DAB standard uses the MPEG-1 Audio Layer II (ISO/IEC 11172-3) for 48 kHz sampling frequency and the MPEG-2 Audio Layer II (ISO/IEC 13818-3) for 24 kHz sampling frequency.

MPEG Audio

In the late 1980s, ISO's Moving Picture Experts Group
Moving Picture Experts Group
The Moving Picture Experts Group is a working group of experts that was formed by ISO and IEC to set standards for audio and video compression and transmission. It was established in 1988 by the initiative of Hiroshi Yasuda and Leonardo Chiariglione, who has been from the beginning the Chairman...

 (MPEG) started an effort to standardize digital audio and video encoding, expected to have a wide range of applications in digital radio and TV broadcasting (later DAB
Digital audio broadcasting
Digital Audio Broadcasting is a digital radio technology for broadcasting radio stations, used in several countries, particularly in Europe. As of 2006, approximately 1,000 stations worldwide broadcast in the DAB format....

, DMB
Digital Multimedia Broadcasting
Digital Multimedia Broadcasting is a digital radio transmission technology developed in South Korea as part of the national IT project for sending multimedia such as TV, radio and datacasting to mobile devices such as mobile phones...

, DVB), and use on CD-ROM (later Video CD
Video CD
Before the advent of DVD and Blu-ray, the Video CD became the first format for distributing films on standard 120 mm optical discs. The format is a standard digital format for storing video on a Compact Disc...

). The MUSICAM audio coding was one of 14 proposals for MPEG-1 Audio standard that were submitted to ISO in 1989.

The MPEG-1 Audio standard was based on the existing MUSICAM and ASPEC audio formats.
The MPEG-1
MPEG-1
MPEG-1 is a standard for lossy compression of video and audio. It is designed to compress VHS-quality raw digital video and CD audio down to 1.5 Mbit/s without excessive quality loss, making video CDs, digital cable/satellite TV and digital audio broadcasting possible.Today, MPEG-1 has become...

 Audio standard included the three audio "layers" (encoding techniques) now known as Layer I (MP1), Layer II (MP2) and Layer III (MP3).
All algorithms for MPEG-1 Audio Layer I, II and III were approved in 1991 as the committee draft of ISO-11172 and finalized in 1992 as part of MPEG-1
MPEG-1
MPEG-1 is a standard for lossy compression of video and audio. It is designed to compress VHS-quality raw digital video and CD audio down to 1.5 Mbit/s without excessive quality loss, making video CDs, digital cable/satellite TV and digital audio broadcasting possible.Today, MPEG-1 has become...

, the first standard suite by MPEG, which resulted in the international standard ISO
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

/IEC
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...

 11172-3 (a.k.a. MPEG-1 Audio or MPEG-1 Part 3), published in 1993. Further work on MPEG audio was finalized in 1994 as part of the second suite of MPEG standards, MPEG-2
MPEG-2
MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission...

, more formally known as international standard ISO/IEC 13818-3 (a.k.a. MPEG-2 Part 3 or backwards compatible MPEG-2 Audio or MPEG-2 Audio BC), originally published in 1995. MPEG-2 Part 3 (ISO/IEC 13818-3) defined additional bit rates and sample rates for MPEG-1 Audio Layer I, II and III. The new sampling rates are exactly half that of those originally defined for MPEG-1 Audio. MPEG-2 Part 3 also enhanced MPEG-1's audio by allowing the coding of audio programs with more than two channels, up to 5.1 multichannel.

The Layer III (MP3
MP3
MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...

) component uses a lossy compression algorithm that was designed to greatly reduce the amount of data required to represent an audio recording and sound like a decent reproduction of the original uncompressed audio for most listeners.

Emmy Award in Engineering

CCETT
Centre commun d'études de télévision et télécommunications
CCETT or Centre commun d'études de télévision et télécommunications was a research centre created in Rennes in 1972 jointly by the Office de Radiodiffusion Télévision Française and Centre National...

 (France), IRT
Institut für Rundfunktechnik
The Institut für Rundfunktechnik GmbH is the research centre of the German broadcasters , Austria's broadcaster and the Swiss public broadcaster . It is located in Munich and is responsible for the research and standardisation of broadcasting technology...

 (Germany) and Philips
Philips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....

 (The Netherlands) won Emmy Award
Emmy Award
An Emmy Award, often referred to simply as the Emmy, is a television production award, similar in nature to the Peabody Awards but more focused on entertainment, and is considered the television equivalent to the Academy Awards and the Grammy Awards .A majority of Emmys are presented in various...

 in Engineering 2000 for development of a digital audio two-channel compression system known as Musicam or MPEG Audio Layer II.

Technical specifications

MPEG-1 Audio Layer II is defined in ISO/IEC 11172-3 (MPEG-1 Part 3)
  • Sampling rate
    Sampling rate
    The sampling rate, sample rate, or sampling frequency defines the number of samples per unit of time taken from a continuous signal to make a discrete signal. For time-domain signals, the unit for sampling rate is hertz , sometimes noted as Sa/s...

    s: 32, 44.1 and 48 kHz
  • Bit rate
    Bit rate
    In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....

    s: 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320 and 384 kbit/s


An extension has been provided in MPEG-2 Audio Layer II and is defined in ISO/IEC 13818-3 (MPEG-2 Part 3)
  • Additional sampling rates: 16, 22.05 and 24 kHz
  • Additional bit rates: 8, 16, 24, 40 and 144 kbit/s
  • Multichannel support
    MPEG Multichannel
    MPEG Multichannel is an extension to the MPEG-1 Layer II audio compression specification, as defined in the MPEG-2 Audio standard , which allows it provide up to 5.1-channels of audio...

     - up to 5 full range audio channels and an LFE-channel (Low Frequency Enhancement channel)


The format is based on successive digital frames of 1152 sampling intervals with four possible formats:
  • mono format
  • stereo format
  • intensity encoded joint stereo format (stereo irrelevance)
  • dual channel (uncorrelated) format


Variable bit rate

MPEG audio may have variable bit rate (VBR), but it is not widely supported. Layer II can use a method called bit rate switching. Each frame may be created with a different bit rate.
According to ISO/IEC 11172-3:1993, Section 2.4.2.3: In order to provide the smallest possible delay and complexity, the (MPEG audio) decoder is not required to support a continuously variable bit rate when in layer I or II.

How the MP2 format works

  • MP2 is a sub-band audio encoder
    Sub-band coding
    Sub-band coding is any form of transform coding that breaks a signal into a number of different frequency bands and encodes each one independently. This decomposition is often the first step in data compression for audio and video signals....

    , which means that compression takes place in the time domain
    Time domain
    Time domain is a term used to describe the analysis of mathematical functions, physical signals or time series of economic or environmental data, with respect to time. In the time domain, the signal or function's value is known for all real numbers, for the case of continuous time, or at various...

     with a low-delay filter bank producing 32 frequency domain components. By comparison, MP3 is a transform audio encoder with hybrid filter bank, which means that compression takes place in the frequency domain
    Frequency domain
    In electronics, control systems engineering, and statistics, frequency domain is a term used to describe the domain for analysis of mathematical functions or signals with respect to frequency, rather than time....

     after a hybrid (double) transformation from the time domain.
  • MPEG Audio Layer II is the core algorithm of the MP3 standards. All psychoacoustical characteristics and frame format structures of the MP3 format are derived from the basic MP2 algorithm and format.
  • The MP2 encoder may exploit inter channel redundancies using optional "joint stereo" intensity encoding.
  • MP2 performs similarly to MP3 on high bit rates (224 to 384 kbit/s) and is considered more error resilient than MP3, so MP2 is often still used for broadcast applications. Typically, private broadcasters worldwide compress their material at 256kbit/s (stereo) while their counterparts in public broadcasting
    Public broadcasting
    Public broadcasting includes radio, television and other electronic media outlets whose primary mission is public service. Public broadcasters receive funding from diverse sources including license fees, individual contributions, public financing and commercial financing.Public broadcasting may be...

     (including the Canadian Broadcasting Corporation
    Canadian Broadcasting Corporation
    The Canadian Broadcasting Corporation, commonly known as CBC and officially as CBC/Radio-Canada, is a Canadian crown corporation that serves as the national public radio and television broadcaster...

    , Channel Africa
    Channel Africa
    Channel Africa is the international broadcasting service of the South African Broadcasting Corporation. Airing on shortwave, satellite radio and Internet radio platforms, the service airs news, cultural, sports and public affairs programming focusing on South Africa and the African...

    , Deutsche Welle
    Deutsche Welle
    Deutsche Welle or DW, is Germany's international broadcaster. The service is aimed at the overseas market. It broadcasts news and information on shortwave, Internet and satellite radio on 98.7 DZFE in 30 languages . It has a satellite television service , that is available in four languages, and...

    , Radio France Internationale
    Radio France Internationale
    Radio France Internationale was created in 1975 as part of Radio France by the Government of France, and replaced the Poste Colonial , Paris Mondial , Radio Paris , RTF Radio Paris and ORTF Radio Paris...

    , Radio Canada International
    Radio Canada International
    Radio Canada International is the international broadcasting service of the Canadian Broadcasting Corporation . Until 1970, it was known as the CBC International Service and was sometimes referred to as the "Voice of Canada" in its early years.- The early years :The idea for creating an...

    , Radio Netherlands
    Radio Netherlands
    Radio Netherlands Worldwide is a public radio and television network based in Hilversum, producing and transmitting programmes for international audiences outside the Netherlands...

    , the SABC, the Singapore Broadcasting Corporation
    Singapore Broadcasting Corporation
    Singapore Broadcasting Corporation was a partially privatised mass market media conglomeration, which dominated the entire television and most of the radio broadcasting industry in Singapore during its existence...

    , and VOA, to cite a few) use 384 kbit/s (although the BBC
    BBC
    The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...

     in the United Kingdom uses 128kbit/s for most of its digital radio broadcasts, the exceptions being Radio 3
    BBC Radio 3
    BBC Radio 3 is a national radio station operated by the BBC within the United Kingdom. Its output centres on classical music and opera, but jazz, world music, drama, culture and the arts also feature. The station is the world’s most significant commissioner of new music, and its New Generation...

     and Radio 7 being broadcast at 192kbit/s and 80kbit/s respectively).

  • Like MP3, MP2 is a perceptual format, 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 according to a psychoacoustic model, which takes into account the parameters of the human auditory system. Research into psychoacoustics
    Psychoacoustics
    Psychoacoustics is the scientific study of sound perception. More specifically, it is the branch of science studying the psychological and physiological responses associated with sound...

     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 ignoring information at frequencies that are deemed to be imperceptible, thus allowing more data to be allocated to the reproduction of perceptible frequencies.
  • 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 in 576 frequency components. Therefore, MP3 has a higher frequency resolution than MP2, which allows the psychoacoustic model to be applied more selectively than for MP2. So MP3 has greater scope to reduce the bit rate.
  • The use of an additional entropy coding tool and this higher frequency accuracy explains why MP3 doesn't need as high a bit rate as MP2 to get an acceptable audio quality. Conversely MP2 shows a better behavior than MP3, in the time domain, due to its lower frequency resolution which implies less codec time delay (simpler editing) and native ruggedness to the digital recording and digital transmission errors.
  • Moreover, the MP2 sub-band filter bank provides an inherent transient concealment feature due to the specific temporal masking effect of its mother filter. This unique characteristic of the MPEG-1 Audio family implies a very good sound quality on audio signals with rapid energy changes such as percussive sounds both on the MP2 and the MP3 formats which use the same basic sub-band filter bank.

Applications of MP2

Part of the DAB
Digital audio broadcasting
Digital Audio Broadcasting is a digital radio technology for broadcasting radio stations, used in several countries, particularly in Europe. As of 2006, approximately 1,000 stations worldwide broadcast in the DAB format....

 digital radio
Digital radio
Digital radio has several meanings:1. Today the most common meaning is digital radio broadcasting technologies, such as the digital audio broadcasting system, also known as Eureka 147. In these systems, the analog audio signal is digitized into zeros and ones, compressed using formats such as...

 and DVB digital television
Digital television
Digital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...

 standards.

Used internally within the radio industry, for example in NPR
NPR
NPR, formerly National Public Radio, is a privately and publicly funded non-profit membership media organization that serves as a national syndicator to a network of 900 public radio stations in the United States. NPR was created in 1970, following congressional passage of the Public Broadcasting...

's PRSS
Public Radio Satellite System
The Public Radio Satellite System is the interconnected satellite-distributed network managed by NPR , and used by NPR, Public Radio International , and American Public Media , as well as independent public radio program producers, to distribute programming via satellite to public radio stations...

 Content Depot programming distribution system.
The Content Depot distributes MPEG-1 L2 audio in a Broadcast Wave File wrapper. MPEG2 with .wav headers is specified in the .wav standards. As a result Windows Media Player will directly play Content Depot files however less intelligent .wav players often do not.

All DVD-Video
DVD-Video
DVD-Video is a consumer video format used to store digital video on DVD discs, and is currently the dominant consumer video format in Asia, North America, Europe, and Australia. Discs using the DVD-Video specification require a DVD drive and a MPEG-2 decoder...

 players in PAL
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...

 countries contain stereo MP2 decoders, making MP2 a possible competitor to Dolby Digital
Dolby Digital
Dolby Digital is the name for audio compression technologies developed by Dolby Laboratories. It was originally called Dolby Stereo Digital until 1994. Except for Dolby TrueHD, the audio compression is lossy. The first use of Dolby Digital was to provide digital sound in cinemas from 35mm film prints...

 in these markets. DVD-Video players in NTSC
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...

 countries are not required to decode MP2 audio, although most do. While some DVD recorder
DVD recorder
A DVD recorder , is an optical disc recorder that uses Optical disc recording technologies to digitally record analog signal or digital signals onto blank writable DVD media...

s store audio in MP2 and many consumer-authored DVDs use the format, commercial DVDs with MP2 soundtracks are rare.

MPEG-1 layer 2 is the standard audio format used in the Video CD
Video CD
Before the advent of DVD and Blu-ray, the Video CD became the first format for distributing films on standard 120 mm optical discs. The format is a standard digital format for storing video on a Compact Disc...

 and Super Video CD
Super Video CD
Super Video CD is a digital format for storing video on standard compact discs. SVCD was intended as a successor to Video CD and an alternative to DVD-Video, and falls somewhere between both in terms of technical capability and picture quality...

 formats (VCD and SVCD also support variable bit rate and MPEG Multichannel
MPEG Multichannel
MPEG Multichannel is an extension to the MPEG-1 Layer II audio compression specification, as defined in the MPEG-2 Audio standard , which allows it provide up to 5.1-channels of audio...

 as added by MPEG-2).

MPEG 1 layer 2 is the standard audio format used in the MHP
Multimedia Home Platform
Multimedia Home Platform is an open middleware system standard designed by the DVB project for interactive digital television. The MHP enables the reception and execution of interactive, Java-based applications on a TV-set. Interactive TV applications can be delivered over the broadcast channel,...

 standard for set-top boxes.

MPEG 1 layer 2 is the audio format used in HDV
HDV
HDV is a format for recording of high-definition video on DV cassette tape. The format was originally developed by JVC and supported by Sony, Canon and Sharp...

 camcorders.

Naming and extensions

The term MP2 and filename extension
Filename extension
A filename extension is a suffix to the name of a computer file applied to indicate the encoding of its contents or usage....

 .mp2 usually refer MPEG-1 Audio Layer II data, but can also refer to MPEG-2 Audio Layer II, a mostly backwards compatible extension which adds support for multichannel audio variable bit rate encoding, and additional sampling rates, defined in ISO/IEC 13818-3. The abbreviation MP2 is also sometimes erroneously applied to MPEG-2
MPEG-2
MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission...

 video or MPEG-2 AAC
Advanced Audio Coding
Advanced Audio Coding is a standardized, lossy compression and encoding scheme for digital audio. Designed to be the successor of the MP3 format, AAC generally achieves better sound quality than MP3 at similar bit rates....

 audio.

See also

  • MPEG-1
    MPEG-1
    MPEG-1 is a standard for lossy compression of video and audio. It is designed to compress VHS-quality raw digital video and CD audio down to 1.5 Mbit/s without excessive quality loss, making video CDs, digital cable/satellite TV and digital audio broadcasting possible.Today, MPEG-1 has become...

    • MPEG-1 Audio Layer I
      MPEG-1 Audio Layer I
      MPEG-1 Audio Layer I, commonly abbreviated to MP1, is one of three audio formats included in the MPEG-1 standard. While supported by most media players, the codec is considered largely outdated, and replaced by MP2 or MP3....

    • MPEG-1 Audio Layer III
      MP3
      MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...

  • MPEG-2
    MPEG-2
    MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission...

  • MP4 (container format)
    MPEG-4 Part 14
    MPEG-4 Part 14 or MP4 is a multimedia container format standard specified as a part of MPEG-4. It is most commonly used to store digital video and digital audio streams, especially those defined by MPEG, but can also be used to store other data such as subtitles and still images...

  • MPEG Elementary stream
    Elementary stream
    An elementary stream as defined by MPEG communication protocol is usually the output of an audio or video encoder. ES contains only one kind of data, e.g. audio, video or closed caption. An elementary stream is often referred to as "elementary", "data", "audio", or "video" bitstreams or streams...

  • Musepack
    Musepack
    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...

    originally MP2-based, with numerous improvements

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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