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Not to be confused with MPEG-4 SLS
MPEG-4 SLS
MPEG-4 SLS, or MPEG-4 Scalable to Lossless as per ISO/IEC 14496-3:2005/Amd 3:2006 , is an extension to the MPEG-4 Part 3 standard to allow lossless audio compression scalable to lossy MPEG-4 General Audio coding methods...

, which is branded HD-AAC.

High-Efficiency Advanced Audio Coding (HE-AAC) is a lossy data compression
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...

 scheme for digital audio
Digital audio
Digital audio is sound reproduction using pulse-code modulation and digital signals. Digital audio systems include analog-to-digital conversion , digital-to-analog conversion , digital storage, processing and transmission components...

 defined as a MPEG-4 Audio profile in ISO/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"...

 14496-3. It is an extension of Low Complexity 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....

 (AAC LC) optimized for low-bitrate
Bitrate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....

 applications such as streaming audio. HE-AAC version 1 profile (HE-AAC v1) uses spectral band replication
Spectral band replication
Spectral band replication is a technology to enhance audio or speech codecs, especially at low bit rates and is based on harmonic redundancy in the frequency domain....

 (SBR) to enhance the compression efficiency 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....

. HE-AAC version 2 profile (HE-AAC v2) couples SBR with Parametric Stereo
Parametric Stereo
Parametric Stereo is a feature and an Audio Object Type defined and used in MPEG-4 Part 3 to further enhance efficiency in low bandwidth stereo media. Advanced Audio Coding Low Complexity combined with Spectral band replication and Parametric Stereo was defined as HE-AAC v2...

 (PS) to enhance the compression efficiency of stereo signals. It is a standardized and improved version of the AACplus codec
Codec
A codec is a device or computer program capable of encoding or decoding a digital data stream or signal. The word codec is a portmanteau of "compressor-decompressor" or, more commonly, "coder-decoder"...

.

HE-AAC is used in 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...

 standards like DAB+ and Digital Radio Mondiale
Digital Radio Mondiale
Digital Radio Mondiale is a set of digital audio broadcasting technologies designed to work over the bands currently used for AM broadcasting, particularly shortwave...

.

History

The progenitor of HE-AAC was developed by Coding Technologies under the trade name CT-aacPlus. CT-aacPlus combined MPEG-2 AAC LC with the Coding Technologies invented spectral band replication
Spectral band replication
Spectral band replication is a technology to enhance audio or speech codecs, especially at low bit rates and is based on harmonic redundancy in the frequency domain....

 (SBR). CT-aacPlus is the codec used by XM Radio for their satellite radio service. Subsequently, Coding Technologies submitted their SBR to MPEG as a basis of HE-AAC.

HE-AAC version 1 was standardized as a profile of MPEG-4 Audio in 2003 by MPEG
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...

 and published as part of MPEG-4 in document ISO/IEC 14496-3:2001/Amd 1:2003. The HE-AAC version 2 profile was standardized in 2006 as ISO/IEC 14496-3:2005/Amd 2:2006.
A parametric stereo coding tool used in HE-AAC v2 was standardized in 2004 by MPEG and published in document ISO/IEC 14496-3:2001/Amd 2:2004.

HE-AAC version 2 was also standardized under the name Enhanced aacPlus by 3GPP
3GPP
The 3rd Generation Partnership Project is a collaboration between groups of telecommunications associations, known as the Organizational Partners...

 for 3G
3G
3G or 3rd generation mobile telecommunications is a generation of standards for mobile phones and mobile telecommunication services fulfilling the International Mobile Telecommunications-2000 specifications by the International Telecommunication Union...

 UMTS multimedia services in September 2004 (3GPP TS 26.401). It is based on the AAC LC, SBR and Parametric Stereo coding tools defined in the MPEG-4 Audio standard (and it refers to ISO/IEC 14496-3:2001/Amd.1:2003 - Bandwidth Extension, ISO/IEC 14496-3:2001/Amd.2:2004 - Parametric Coding for High Quality Audio, ISO/IEC 14496-3:2001 and ISO/IEC 14496-3:2001/Amd.1:2003/DCOR1). In addition it includes further tools such as error concealment, spline resampler, and stereo-to-mono downmix. It was also published by ETSI as TS 126 401 V6.1.0 in December 2004.

Prior to the standardization of HE AAC v2 by MPEG, Coding Technologies submitted the combination of HE-AAC v1 coupled with Parametric Stereo
Parametric Stereo
Parametric Stereo is a feature and an Audio Object Type defined and used in MPEG-4 Part 3 to further enhance efficiency in low bandwidth stereo media. Advanced Audio Coding Low Complexity combined with Spectral band replication and Parametric Stereo was defined as HE-AAC v2...

 under the name Enhanced AAC+. As a result, aacPlus v2 and eAAC+ are now common trade names that refer to HE-AAC v2. AAC+ and aacPlus are common trade names that refer to HE-AAC v1.

Perceived quality

Scientific testing by the European Broadcasting Union
European Broadcasting Union
The European Broadcasting Union is a confederation of 74 broadcasting organisations from 56 countries, and 49 associate broadcasters from a further 25...

 has indicated that HE-AAC at 48 kbit/s was ranked as "Excellent" quality using the MUSHRA
MUSHRA
MUSHRA stands for MUltiple Stimuli with Hidden Reference and Anchor and is a methodology for subjective evaluation of audio quality, to evaluate the perceived quality of the output from lossy audio compression algorithms. It is defined by ITU-R recommendation BS.1534-1. The MUSHRA methodology is...

 scale. 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...

 in the same testing received a score less than half that of HE-AAC and was ranked "Poor" using the MUSHRA scale. Data from this testing also indicated that some individuals confused 48 kbit/s encoded
Code
A code is a rule for converting a piece of information into another form or representation , not necessarily of the same type....

 material with an uncompressed original.

Testing indicates that material decoded from 64 kbit/s HE-AAC does not yet have similar audio quality to material decoded from MP3 at 128 kbit/s using high quality encoders. The test, taking bitrate distribution and RMSD into account, is a tie between MP3pro
Mp3PRO
mp3PRO is an audio compression algorithm that combines the MP3 audio format with spectral band replication compression methods. It claims to achieve transparency at lower bitrates than MP3, resulting in a file nearly half the size of standard MP3...

, HE AAC and Ogg Vorbis.

Further controlled testing by 3GPP
3GPP
The 3rd Generation Partnership Project is a collaboration between groups of telecommunications associations, known as the Organizational Partners...

 during their revision 6 specification process indicates that HE-AAC and its derivative MPEG-4
MPEG-4
MPEG-4 is a method of defining compression of audio and visual digital data. It was introduced in late 1998 and designated a standard for a group of audio and video coding formats and related technology agreed upon by the ISO/IEC Moving Picture Experts Group under the formal standard ISO/IEC...

 HE-AAC v2 provide "Good" audio quality for music at low bit rates (e.g. 24 kbit/s).

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...

 and MPEG-4 AAC LC decoders without SBR support will decode the AAC LC part of the audio, resulting in audio output with only half the sampling frequency, thereby reducing the audio bandwidth. This usually results in the high-end, or treble
Treble (sound)
Treble refers to tones of high frequency or range. In music this corresponds to high notes, and for this reason the treble clef is often used for instruments with higher pitch. Examples of treble sounds are guitar tones, female voice , young boy voice, etc. They have frequencies above 9 KHz. Treble...

, portion of the audio signal missing from the audio product.

Encoding

Sony supports HE-AAC encoding since SonicStage version 4. iTunes 9 supports HE-AAC encoding and playback. Nero
Nero AG
Nero is a global computer software company headquartered in Karlsbad, Germany. It is perhaps most well-known for its burning software, Nero Burning ROM.-History:The company was founded as Ahead Software GmbH in 1995 by Richard Lesser....

 has released a free-of-charge command line HE-AAC encoder, and also supports HE-AAC inside the Nero software suite. Sorenson Media’s Squeeze Compression Suite includes an HE-AACv1 encoder and is available for Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

 as well as Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

. The 3GPP
3GPP
The 3rd Generation Partnership Project is a collaboration between groups of telecommunications associations, known as the Organizational Partners...

 consortium released source code of a reference HE-AACv2 encoder that appears to offer competitive quality. Winamp
Winamp
Winamp is a media player for Windows-based PCs and Android devices, written by Nullsoft, now a subsidiary of AOL. It is proprietary freeware/shareware, multi-format, extensible with plug-ins and skins, and is noted for its graphical sound visualization, playlist, and media library features.Winamp...

 Pro also supports ripping music to HE-AAC. Using a transcoding plugin for Winamp's media library, any file can be transcoded to HE-AAC. XLD, an OS X audio encoding program, offers encoding from any of its supported formats to HE-AAC. Nokia PC Suite
Nokia PC Suite
Nokia PC Suite is a software package used to establish an interface between Nokia mobile devices and computers that run Microsoft Windows operating system.-Usage:...

 may encode audiofiles to eAAC+ format before transmitting them to mobile phone.

Decoding

HE-AAC is supported in the open source
Open source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...

 FAAD/FAAD2 decoding library (and all players incorporating it): VLC media player
VLC media player
VLC media player is a free and open source media player and multimedia framework written by the VideoLAN project.VLC is a portable multimedia player, encoder, and streamer supporting many audio and video codecs and file formats as well as DVDs, VCDs, and various streaming protocols. It is able to...

, Winamp
Winamp
Winamp is a media player for Windows-based PCs and Android devices, written by Nullsoft, now a subsidiary of AOL. It is proprietary freeware/shareware, multi-format, extensible with plug-ins and skins, and is noted for its graphical sound visualization, playlist, and media library features.Winamp...

, foobar2000
Foobar2000
foobar2000 is a freeware audio player for Windows developed by Peter Pawlowski, a former freelance contractor for Nullsoft. It is known for its highly modular design and extensive SDK which allows third-party developers to do such things as completely replace the interface...

, Audacious Media Player
Audacious Media Player
Audacious is a free software audio player with a focus on low resource usage, high audio quality, and support for a wide range of audio formats. It is designed primarily for use on POSIX-compatible systems such as Linux, with limited support for Microsoft Windows...

, and Sony's latest SonicStage
SonicStage
SonicStage is the name for Sony software that is used for managing portable devices when they are plugged into a computer running Microsoft Windows. It comprises a music player and library manager, similar to iTunes, Windows Media Player and RealPlayer. It is used to manage the library of ATRAC...

 version 4. HE-AAC is also used by AOL Radio
AOL Radio
AOL Radio powered by Slacker, , is an online radio service available only in the United States.- Roots :...

 and Pandora Radio clients to deliver high-fidelity music at low bitrates.

Adobe's Flash Player 9 supports HE-AACv2.

iTunes 9.2 and iOS4 include full decoding of HE-AAC v2 parametric stereo streams. iTunes 9 thru 9.1, iPhone OS 3.1 and Fall 2009 iPods have support for HE-AAC playback for version 1 with no parametric stereo. Other third-party software featuring support for HE-AAC include FStream, VLC (without metadata/title streaming), Songbird
Songbird (software)
Songbird is a free and open source software audio player and web browser, with a stated mission "to incubate Songbird, the first Web player, to catalyze and champion a diverse, open Media Web."...

, Snowtape, and recent development versions of Audacious Media Player.

Older versions of Apple iTunes
ITunes
iTunes is a media player computer program, used for playing, downloading, and organizing digital music and video files on desktop computers. It can also manage contents on iPod, iPhone, iPod Touch and iPad....

, iPod Touch
IPod Touch
The iPod Touch is a portable media player, personal digital assistant, handheld game console, and Wi-Fi mobile device designed and marketed by Apple Inc. The iPod Touch adds the multi-touch graphical user interface to the iPod line...

, and iPhone
IPhone
The iPhone is a line of Internet and multimedia-enabled smartphones marketed by Apple Inc. The first iPhone was unveiled by Steve Jobs, then CEO of Apple, on January 9, 2007, and released on June 29, 2007...

 will play HE-AAC files at reduced fidelity because they ignore the spectral-band replication and parametric stereo information, instead playing them as though they were standard AAC-LC files without the high-frequency, or "treble," information that is only present in the SBR part of the signal. These will report the track length as twice its actual length.

Dolby released Dolby Pulse decoders and encoders in September 2008. HE-AAC v2 is the core of Dolby Pulse so files and streams encoded in Dolby Pulse will playback on AAC, HE-AAC v1 and v2 decoders. Conversely files and streams encoded in AAC, HE-AAC v1 or v2 will playback on Dolby Pulse decoders.

Dolby Pulse provides the following additional capabilities beyond HE-AAC v2:
  • Ability to intelligently generate and insert reversible loudness normalization and dynamic range metadata into the encoded file/stream; this metadata can then be used to optimize the playback experience based on application and/or device.
  • Ability to insert custom metadata into the encoded file, and extract this metadata on playback


Dolby has additionally released a PC decoder as an SDK suitable for integration into PC applications requiring Dolby Pulse, HE-AAC or AAC playback capabilities.

Commercial trademarks and labeling

HE-AAC is marketed under the trademark aacPlus(tm) by Coding Technologies and under the trademark Nero Digital(tm) by Nero AG. Sony Ericsson, Nokia and Samsung use AAC+ to label support for HE AAC v1 and eAAC+ to label support for HE-AAC v2 on their phones. Motorola uses AAC+ to indicate HE AAC v1 and "AAC+ Enhanced" to indicate HE AAC v2.

Licensing and patents

Companies holding patents for HE AAC have formed a patent pool
Patent pool
In patent law, a patent pool is a consortium of at least two companies agreeing to cross-license patents relating to a particular technology. The creation of a patent pool can save patentees and licensees time and money, and, in case of blocking patents, it may also be the only reasonable method...

 administered by Via Licensing Corporation to provide a single point of license for product makers.

Patent licenses are required for end-product companies that make hardware or software products that include HE AAC encoders and/or decoders. Unlike the MP3 format, content owners are not required to pay license fees to distribute content in HE AAC.

Standards

HE-AAC profile was first standardized in ISO/IEC 14496-3:2001/Amd 1:2003. HE-AAC v2 profile (HE-AAC with Parametric Stereo) was first specified in ISO/IEC 14496-3:2005/Amd 2:2006. The Parametric Stereo coding tool used by HE-AAC v2 was standardized in 2004 and published as ISO/IEC 14496-3:2001/Amd 2:2004.

The current version of the MPEG-4 Audio (including HE-AAC standards) is published in ISO/IEC 14496-3:2009.

Enhanced aacPlus is required audio compression format in 3GPP
3GPP
The 3rd Generation Partnership Project is a collaboration between groups of telecommunications associations, known as the Organizational Partners...

 technical specifications for 3G
3G
3G or 3rd generation mobile telecommunications is a generation of standards for mobile phones and mobile telecommunication services fulfilling the International Mobile Telecommunications-2000 specifications by the International Telecommunication Union...

 UMTS multimedia services and should be supported in IP Multimedia Subsystem
IP Multimedia Subsystem
The IP Multimedia Subsystem or IP Multimedia Core Network Subsystem is an architectural framework for delivering Internet Protocol multimedia services. It was originally designed by the wireless standards body 3rd Generation Partnership Project , as a part of the vision for evolving mobile...

 (IMS), Multimedia Messaging Service
Multimedia Messaging Service
Multimedia Messaging Service, or MMS, is a standard way to send messages that include multimedia content to and from mobile phones. It extends the core SMS capability that allowed exchange of text messages only up to 160 characters in length.The most popular use is to send photographs from...

 (MMS), Multimedia Broadcast/Multicast Service
Multimedia Broadcast Multicast Service
Multimedia Broadcast Multicast Services is a point-to-multipoint interface specification for existing and upcoming 3GPP cellular networks, which is designed to provide efficient delivery of broadcast and multicast services, both within a cell as well as within the core network...

 (MBMS) and Transparent end-to-end Packet-switched Streaming Service (PSS). HE-AAC version 2 was standardized under the name Enhanced aacPlus by 3GPP
3GPP
The 3rd Generation Partnership Project is a collaboration between groups of telecommunications associations, known as the Organizational Partners...

 for 3G UMTS multimedia services in September 2004 (3GPP TS 26.401).

HE-AAC and HE-AAC v2 audio coding for DVB applications is standardized by TS 101 154. AacPlus v2 by Coding Technologies is also standardized by the ETSI
European Telecommunications Standards Institute
The European Telecommunications Standards Institute is an independent, non-profit, standardization organization in the telecommunications industry in Europe, with worldwide projection...

 as TS 102 005 for Satellite services to Handheld devices (DVB-SH) below 3 GHz.

In December 2007, Brazil started broadcasting terrestrial DTV standard called International ISDB-Tb
ISDB-Tb
ISDB-Tb is the short for International System for Digital Broadcast, Terrestrial, Brazilian version.It is a Digital TV system based on Japanese ISDB-T . ISDB-Tb system is also known as SBTVD and is used in Brazil...

 that implements video coding H.264 with audio AAC LC on main program (single or multi) and video H.264 with audio HE-AACv2 in the 1Seg mobile sub-program.

Versions

The following is the summary of the different versions of HE-AAC:
Version Common trade names Codec feature Standards
> aacPlus v1, eAAC, AAC+, CT-aacPlus
| AAC LC + SBR
| ISO/IEC 14496-3:2001/Amd 1:2003
> aacPlus v2, eAAC+, AAC++, Enhanced AAC+
| AAC LC + SBR + PS
| ISO/IEC 14496-3:2005/Amd 2:2006

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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