High Efficiency AAC (HE-AAC) is a lossy data compression scheme for digital audio. A lossy compression method is one where compressing data and then decompressing it retrieves data that may well be different from the original but is close enough to be useful Digital audio uses Digital signals for Sound reproduction. This includes analog-to-digital conversion, digital-to-analog conversion, storage It is an extension of Low Complexity AAC (AAC LC) optimized for low-bitrate applications such as streaming audio. Advanced Audio Coding ( AAC) is a standardized lossy compression and encoding scheme for Digital audio. In Telecommunications and Computing, bitrate (sometimes written bit rate, data rate or as a Variable R or f b Streaming multimedia is Multimedia that is constantly received by and normally presented to an end-user while it is being delivered by a streaming provider (the HE-AAC version 1 (HE-AAC v1) uses Spectral Band Replication (SBR) to enhance the compression efficiency in the frequency domain. Spectral band replication ( SBR) is a technology to enhance audio or Speech codecs especially at low Bit rates and is based on harmonic redundancy in the HE-AAC version 2 (HE-AAC v2) couples SBR with Parametric Stereo (PS) to enhance the compression efficiency of stereo signals. Parametric Stereo is a feature used in Advanced Audio Coding to further enhance efficiency in low bandwidth stereo media
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History
HE-AAC version 1 was standardized in 2003 by MPEG and published as part of MPEG-4 in document ISO/IEC 14496-3, Amd. The Moving Picture Experts Group, commonly referred to as simply MPEG, is a Working group of ISO / IEC charged with the development of video and 1:2003. HE AAC version 2 was standardized in 2004 by MPEG and published as part of MPEG-4 in document ISO/IEC 14496-3, Amd. 2:2004
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 (SBR). Spectral band replication ( SBR) is a technology to enhance audio or Speech codecs especially at low Bit rates and is based on harmonic redundancy in the 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.
Later, but prior to the standardization of HE AAC v2 by MPEG, Coding Technologies submitted the combination of HE-AAC v1 coupled with Parametric Stereo to 3GPP under the name Enhanced AAC+. Parametric Stereo is a feature used in Advanced Audio Coding to further enhance efficiency in low bandwidth stereo media As a result, aacPlus v2 and eAAC+ are now common trade names which refer to HE-AAC v2. AAC+ and aacPlus are common trade names which refer to HE-AAC v1.
Perceived quality
Scientific testing by the European Broadcasting Union has indicated that HE-AAC at 48 kbit/s was ranked as "Excellent" quality using the MUSHRA scale. The European Broadcasting Union ( EBU; L'Union Européenne de Radio-Télévision ("UER" and unrelated to the European Union) is a confederation 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 [1]. MP3 in the same testing received a score less than half that of HE-AAC and was ranked "Poor" using the MUSHRA scale. MPEG-1 Audio Layer 3, more commonly referred to as MP3, is a Digital audio encoding format using a form of Lossy data compression Data from this testing also indicated that some individuals confused 48 kbit/s encoded material with an uncompressed original. In Communications a code is a rule for converting a piece of Information (for example a letter, Word, Phrase, or For processes which reduce the amount of time it takes to listen to and understand a recording see Time-compressed speech.
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[2]. The test, taking bitrate distribution and RMSD into account, is a tie between MP3pro, HE AAC and the open-source Ogg Vorbis. The root mean square deviation (RMSD ( also root mean square error (RMSE) is a frequently-used measure of the differences between values predicted by a model mp3PRO is an Audio compression algorithm (or Codec) that combines the MP3 audio format with Spectral band replication compression methods Vorbis is a free and open source, lossy audio Codec project headed by the Xiph
Further controlled testing by 3GPP during their revision 6 specification process indicates that HE-AAC and its derivative MPEG-4 HE-AAC v2 provide "Good" audio quality for music at low bit rates (e. The 3rd Generation Partnership Project ( 3GPP) is a collaboration between groups of telecommunications associations to make a globally applicable third generation ( 3G MPEG-4 is a collection of methods defining compression of audio and visual (AV digital data g. 24 kbit/s).
MPEG-2 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. MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information" No known tests have been conducted which compare the audio quality of such decoded material.
HE-AAC today competes only with Microsoft's low-bitrate WMA Professional codec. Microsoft Corporation is an American multinational Computer technology Corporation, which rose to dominate the Home computer Windows Media Audio ( WMA) is an Audio data compression technology developed by Microsoft. [3] [4] [5] [6]
Support
HE-AAC is supported in the open source FAAD/FAAD2 decoding library (and all players incorporating it): VLC media player, Winamp, foobar2000, Audacious Media Player, and Sony's latest SonicStage version 4. Open source is a development methodology which offers practical accessibility to a product's source (goods and knowledge Winamp is a proprietary media player written by Nullsoft, now a subsidiary of Time Warner. foobar2000 is a Freeware audio player for Windows developed by Peter Pawlowski, a former freelance contractor for Nullsoft. Audacious is a GUI -based Free software media player for POSIX systems such as Linux. SonicStage is the name for Sony software that is used for managing portable devices when they are plugged into a computer running Microsoft Windows. HE-AAC is also used by AOL Radio clients to deliver high-fidelity music at low bitrates.
As of 2007, neither iTunes, nor the iPod supports HE-AAC. iTunes is a proprietary digital media player application introduced by Apple Inc iPod is a popular brand of Portable media players designed and marketed by Apple Inc Only MPEG 2 AAC (MPEG-4 Audio - part 3) is supported so the only players for Mac OS X are FStream, VLC (without metadata/title streaming), Songbird, and recent development versions of Audacious Media Player. Mac OS X (mæk oʊ ɛs tɛn is a line of computer Operating systems developed marketed and sold by Apple Inc, the latest of which is pre-loaded on all currently Songbird is a Free software media player and Web browser developed by a group known as Pioneers of the Inevitable (with members who previously
Nero has released a free of charge command line HE-AAC encoder, and also supports HE-AAC inside the Nero software suite. Nero AG is a German software company based in Karlsbad, Germany. Sorenson Media’s Squeeze Compression Suite includes an HE-AACv1 encoder and is available for Mac OS X as well as Windows. Mac OS X (mæk oʊ ɛs tɛn is a line of computer Operating systems developed marketed and sold by Apple Inc, the latest of which is pre-loaded on all currently Microsoft Windows is a series of Software Operating systems and Graphical user interfaces produced by Microsoft. Adobe's Flash Player 9 supports HE-AACv2. The Adobe Flash Player is a widely distributed proprietary multimedia and application player created by Macromedia and now developed and distributed by Adobe
Lastly, the 3GPP consortium released source code of a reference HE-AACv2 encoder that appears to be quite competitive regarding quality[7]. The 3rd Generation Partnership Project ( 3GPP) is a collaboration between groups of telecommunications associations to make a globally applicable third generation ( 3G No community-supported Free Software encoder is available yet. Free software or software libre is Software that can be used studied and modified without restriction and which can be copied and redistributed in modified or unmodified
Promotion aspects
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 v1[8] have formed a patent pool under Via Licensing to provide a single point of license for product makers. Patents owned by Coding Technologies and Philips covering the Parametric Stereo used in HE AAC v2 are not included in the Via Licensing pool and are licensed separately by Coding Technologies. [9]
Patent licenses are required for end-product companies making hardware or software products which include HE AAC encoders and/or decoders. [10] Unlike the MP3 format [11], content owners are not required to pay license fees to distribute content in HE AAC.
Standards
HE-AAC was first standardized in ISO/IEC 14496-3:2001/Amd. 1. HE-AAC v2 (AAC with Parametric Stereo) was first specified in ISO/IEC 14496-3:2001/Amd. 4. [12]
The current version of the HE-AAC standard is ISO/IEC 14496-3:2005 (with 14496-3:2005/Amd. 2. for HE-AAC v2[13])
AacPlus v2 by Codingtechnologies [12] is also standardized by ETSI (European Telecommunications Standards Institute) as TS 102005 for Satellite services to Handheld devices (DVB-SH) below 3 GHz. The European Telecommunications Standards Institute ( ETSI) is an independent non-for-profit Standardization organization of the Telecommunications The European Telecommunications Standards Institute ( ETSI) is an independent non-for-profit Standardization organization of the Telecommunications
In December 2007, Brazil started broadcasting terrestrial DTV standard called International ISDB-Tb that implements video coding H. 264AVC with audio AAC-LC on main program(single or multi) and video H. 264AVC with audio HE-AACv2 in the 1Seg mobile sub-program.
Versions
The following is the summary of the different version of HE-AAC:
| Version | Common trade names | Codec feature | Standards |
|---|---|---|---|
| HE-AAC v1 | AAC+, aacPlus v1, CT-aacPlus | AAC LC + SBR | ISO/IEC 14496-3:2003/Amd. 1 |
| HE-AAC v2 | aacPlus v2, eAAC+, Enhanced AAC+, AAC++ | AAC LC + SBR + PS | ISO/IEC 14496-3:2005/Amd. 2 |
See also
References
- ^ http://www.ebu.ch/CMSimages/en/tec_doc_t3296_tcm6-10497.pdf
- ^ Results of 64kbit/s Listening Test
- ^ Multiformat Listening Test @ 48 kbps - FINISHED - Hydrogenaudio Forums
- ^ Comparing Windows Media Audio Professional and HE AAC Audio Coding
- ^ 80 kbps personal listening test (summer 2005) - Hydrogenaudio Forums
- ^ MP3 WMA AAC OGG qualité à 96 kbps (évaluation) - Traitement Audio - Video & Son - FORUM HardWare.fr
- ^ MP3' Tech - 48kbps AAC public test results
- ^ Via Licensing
- ^ Coding Technologies | licensing || aacPlus
- ^ Via Licensing
- ^ Thomson. Windows Media Audio ( WMA) is an Audio data compression technology developed by Microsoft. Thomson/FhG MP3 Licensing.
- ^ a b http://www.codingtechnologies.com/products/assets/CT_aacPlus_whitepaper.pdf
- ^ ISO/IEC 14496-3:2005/Amd. 2 [1]
External links
- MPEG-4 HE-AAC v2 — audio coding for today's digital media world, article in the EBU technical review (01/2006) giving explanations on HE-AAC. The European Broadcasting Union ( EBU; L'Union Européenne de Radio-Télévision ("UER" and unrelated to the European Union) is a confederation
- Tuner2.com list of Internet radio stations using aacPlus
- RadioFeeds UK & Ireland (AAC+) UK terrestrial radio stations streaming online in aacPlus format
- aacPlus explained
- Open Source AAC codec FAAC (encoder) and FAAD2 (decoder)
- Easy CD-DA Extractor CD-Ripper that supports aacPlus and AAC in ripping, encoding, decoding, and burning.
- Winamp.com Audio player/ripper that allows you to rip CDs into HE-AAC and convert other audio files into HE-AAC (with a free add-on).
- mp3PRO vs MP3 - includes graphs comparing high-frequency performance for MP3pro (similar to HE-AAC+)
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