Editing Advanced Audio Coding (section)

===Standardization===
{{Confusing section|date=April 2025}}
In 1997, AAC was first introduced as ''MPEG-2 Part 7'', formally known as ''[[ISO]]/[[IEC]] 13818-7:1997''. This part of MPEG-2 was a new part, since MPEG-2 already included ''MPEG-2 Part 3'', formally known as ''ISO/IEC 13818-3: MPEG-2 BC'' (Backwards Compatible).<ref name="mpeg-bc">{{cite web | url=http://www.mpeg.org/MPEG/audio/aac.html | title=AAC | website=MPEG.ORG | access-date=2009-10-28 | archive-url=https://web.archive.org/web/20091003042614/http://www.mpeg.org/MPEG/audio/aac.html | archive-date=3 October 2009 | url-status=dead }}</ref><ref name="iso13818-7-2006-pdf">{{cite web | url=http://webstore.iec.ch/preview/info_isoiec13818-7%7Bed4.0%7Den.pdf | title=ISO/IEC 13818-7, Fourth edition, Part 7 - Advanced Audio Coding (AAC) | publisher=[[ISO]] | date=15 January 2006 | access-date=2009-10-28 | url-status=live | archive-url=https://web.archive.org/web/20090306055335/http://webstore.iec.ch/preview/info_isoiec13818-7%7Bed4.0%7Den.pdf | archive-date=6 March 2009 }}</ref> Therefore, MPEG-2 Part 7 is also known as ''MPEG-2 NBC'' (Non-Backward Compatible), because it is not compatible with the [[MPEG-1]] audio formats ([[MP1]], [[MPEG-1 Audio Layer II|MP2]] and [[MP3]]).<ref name="mpeg-bc" /><ref>{{cite web | url=http://www.mp3-tech.org/aac.html | title=MPEG-2/MPEG-4 - AAC | year=2003 | first=Gabriel | last=Bouvigne | publisher=MP3'Tech | access-date=2009-10-28 | url-status=live | archive-url=https://web.archive.org/web/20100105022907/http://www.mp3-tech.org/aac.html | archive-date=2010-01-05 }}</ref><ref name="mpeg-audio-faq-bc">{{cite web | url=http://mpeg.chiariglione.org/faq/mp1-aud/mp1-aud.htm | title=MPEG Audio FAQ Version 9 - MPEG-1 and MPEG-2 BC | publisher=[[ISO]] | date=October 1998 | access-date=2009-10-28 | url-status=live | archive-url=https://web.archive.org/web/20100218081343/http://mpeg.chiariglione.org/faq/mp1-aud/mp1-aud.htm | archive-date=2010-02-18 }}</ref><ref name="mpeg-audio-florence">{{cite web|url=http://mpeg.chiariglione.org/meetings/firenze/prfloren.htm |title=Florence Press Release |publisher=[[ISO]] |date=March 1996 |access-date=2009-10-28 |url-status=dead |archive-url=https://web.archive.org/web/20100408061828/http://mpeg.chiariglione.org/meetings/firenze/prfloren.htm |archive-date=2010-04-08 }}</ref>

MPEG-2 Part 7 defined three profiles: ''Low-Complexity'' profile (AAC-LC / LC-AAC), ''Main'' profile (AAC Main) and ''Scalable Sampling Rate'' profile (AAC-SSR). AAC-LC profile consists of a base format very much like AT&T's Perceptual Audio Coding (PAC) coding format,<ref>Johnston, J. D. and Ferreira, A. J., "Sum-difference stereo transform coding", ICASSP '92, March 1992, pp. II-569-572.</ref><ref>Sinha, D. and Johnston, J. D., "Audio compression at low bit rates using a signal adaptive switched filterbank", IEEE ASSP, 1996, pp. 1053-1057.</ref><ref>Johnston, J. D., Sinha, D., Dorward, S. and Quackenbush, S., "AT&T perceptual audio coder (PAC)" in Collected Papers on Digital Audio Bit-Rate Reduction, Gilchrist, N. and Grewin, C. (Ed.), Audio Engineering Society, 1996.</ref> with the addition of [[temporal noise shaping]] (TNS),<ref>Herre, J. and Johnston, J. D., "Enhancing the performance of perceptual audio coders by using temporal noise shaping", AES 101st Convention, no. preprint 4384, 1996</ref> the [[Kaiser window]] (described below), a nonuniform [[quantizer]], and a reworking of the bitstream format to handle up to 16 stereo channels, 16 mono channels, 16 low-frequency effect (LFE) channels and 16 commentary channels in one bitstream. The Main profile adds a set of recursive predictors that are calculated on each tap of the filterbank. The [[Scalable Samping Rate Profile|SSR]] uses a 4-band [[Pseudo Quadrature Mirror Filter|PQMF]] filterbank, with four shorter filterbanks following, in order to allow for scalable sampling rates.

In 1999, MPEG-2 Part 7 was updated and included in the MPEG-4 family of standards and became known as ''[[MPEG-4 Part 3]]'', ''MPEG-4 Audio'' or ''ISO/IEC 14496-3:1999''. This update included several improvements. One of these improvements was the addition of ''[[MPEG-4 Part 3#MPEG-4 Audio Object Types|Audio Object Types]]'' which are used to allow interoperability with a diverse range of other audio formats such as [[TwinVQ]], [[CELP]], [[HVXC]], [[speech synthesis]] and [[MPEG-4 Structured Audio]]. Another notable addition in this version of the AAC standard is ''Perceptual Noise Substitution'' (PNS). In that regard, the AAC profiles (AAC-LC, AAC Main and AAC-SSR profiles) are combined with perceptual noise substitution and are defined in the MPEG-4 audio standard as Audio Object Types.<ref name="mpeg4audio-profiles">{{cite web|url=http://mpeg.chiariglione.org/tutorials/papers/icj-mpeg4-si/09-natural_audio_paper/profiles.html |title=MPEG-4 Natural Audio Coding - Audio profiles and levels |first1=Karlheinz |last1=Brandenburg |first2=Oliver |last2=Kunz |first3=Akihiko |last3=Sugiyama |website=chiariglione.org |access-date=2009-10-06 |url-status=dead |archive-url=https://web.archive.org/web/20100717130019/http://mpeg.chiariglione.org/tutorials/papers/icj-mpeg4-si/09-natural_audio_paper/profiles.html |archive-date=2010-07-17 }}</ref> MPEG-4 Audio Object Types are combined in four MPEG-4 Audio profiles: Main (which includes most of the MPEG-4 Audio Object Types), Scalable (AAC LC, AAC LTP, CELP, HVXC, TwinVQ, Wavetable Synthesis, TTSI), Speech (CELP, HVXC, TTSI) and Low Rate Synthesis (Wavetable Synthesis, TTSI).<ref name="mpeg4audio-profiles" /><ref name="mpeg4audio-version1-draft">{{cite web | url=https://www.itscj.ipsj.or.jp/sc29/open/29view/29n2603t0.pdf | title=ISO/IEC FCD 14496-3 Subpart 1 - Draft - N2203 | publisher=[[ISO]]/[[IEC]] JTC 1/SC 29/WG 11 | date=15 May 1998 | access-date=2009-10-07 }}</ref>

The reference software for MPEG-4 Part 3 is specified in MPEG-4 Part 5 and the conformance bit-streams are specified in MPEG-4 Part 4. MPEG-4 Audio remains [[backward-compatible]] with MPEG-2 Part 7.<ref name="mpeg4audio-mpeg2audio">{{cite web|url=http://mpeg.chiariglione.org/tutorials/papers/icj-mpeg4-si/09-natural_audio_paper/gacoding.html |title=MPEG-4 Natural Audio Coding - General Audio Coding (AAC based) |first1=Karlheinz |last1=Brandenburg |first2=Oliver |last2=Kunz |first3=Akihiko |last3=Sugiyama |website=chiariglione.org |year=1999 |access-date=2009-10-06 |url-status=dead |archive-url=https://web.archive.org/web/20100219233137/http://mpeg.chiariglione.org/tutorials/papers/icj-mpeg4-si/09-natural_audio_paper/gacoding.html |archive-date=2010-02-19 }}</ref>

The MPEG-4 Audio Version 2 (ISO/IEC 14496-3:1999/Amd 1:2000) defined new audio object types: the low delay AAC ([[AAC-LD]]) object type, bit-sliced arithmetic coding (BSAC) object type, parametric audio coding using [[Harmonic and Individual Lines and Noise|harmonic and individual line plus noise]] and error resilient (ER) versions of object types.<ref name="mpeg4audio-iso-2-amd">{{cite web | url=http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=31568 | title=ISO/IEC 14496-3:1999/Amd 1:2000 - Audio extensions | publisher=[[ISO]] | year=2000 | access-date=2009-10-07 | url-status=live | archive-url=https://web.archive.org/web/20110606215234/http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=31568 | archive-date=2011-06-06 }}</ref><ref name="mpeg4audio-version2">{{Cite FTP | url=ftp://ftp.tnt.uni-hannover.de/pub/MPEG/audio/mpeg4/documents/w2803/w2803_n.pdf | title=ISO/IEC 14496-3:/Amd.1 - Final Committee Draft - MPEG-4 Audio Version 2 | date=July 1999 | access-date=2009-10-07 | url-status=dead | server=[[ISO]]/[[IEC]] JTC 1/SC 29/WG 11 }}</ref><ref name="mpeg4audio2">{{cite web|url=https://sound.media.mit.edu/resources/mpeg4/audio/general/aes108_6-Parametric.pdf|title=MPEG-4 Version 2 Audio Workshop:HILN - Parametric Audio Coding|at=AES 108th Convention: MPEG-4 Version 2 Audio What is it about?|location=Paris| first1=Heiko |last1=Purnhagen | date=19 February 2000 | access-date=2009-10-07}}</ref> It also defined four new audio profiles: High Quality Audio Profile, Low Delay Audio Profile, Natural Audio Profile and Mobile Audio Internetworking Profile.<ref name="mpeg4-profiles">{{cite web|url=http://www.m4if.org/resources/profiles/audio.php |archive-url=http://webarchive.loc.gov/all/20100108152236/http://www.m4if.org/resources/profiles/audio.php |url-status=dead |archive-date=2010-01-08 |title=Levels for Audio Profiles |first1=Fernando |last1=Pereira |publisher=MPEG Industry Forum |date=October 2001 |access-date=2009-10-15 }}</ref>

The [[HE-AAC]] Profile (AAC LC with [[Spectral band replication|SBR]]) and AAC Profile (AAC LC) were first standardized in ISO/IEC 14496-3:2001/Amd 1:2003.<ref name="he-aac-amd1">{{cite web | url=http://www.iso.org/iso/catalogue_detail.htm?csnumber=38148 | title=ISO/IEC 14496-3:2001/Amd 1:2003 - Bandwidth extension | publisher=[[ISO]] | year=2003 | access-date=2009-10-07 | url-status=live | archive-url=https://web.archive.org/web/20110606054451/http://www.iso.org/iso/catalogue_detail.htm?csnumber=38148 | archive-date=2011-06-06 }}</ref> The HE-AAC v2 Profile (AAC LC with SBR and Parametric Stereo) was first specified in ISO/IEC 14496-3:2005/Amd 2:2006.<ref name="mpeg4audio-n7016">{{cite web|url=http://kikaku.itscj.ipsj.or.jp/sc29/open/29view/29n6475t.doc |title=Text of ISO/IEC 14496-3:2001/FPDAM 4, Audio Lossless Coding (ALS), new audio profiles and BSAC extensions |format=DOC |publisher=[[ISO]]/[[IEC]] JTC1/SC29/WG11/N7016 |date=11 January 2005 |access-date=2009-10-09 |url-status=dead |archive-url=https://web.archive.org/web/20140512215821/http://kikaku.itscj.ipsj.or.jp/sc29/open/29view/29n6475t.doc |archive-date=12 May 2014 }}</ref><ref name="ISO 14496-3:2005/Amd.2">{{cite web | title=Audio Lossless Coding (ALS), new audio profiles and BSAC extensions, ISO/IEC 14496-3:2005/Amd 2:2006 | url=http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=43026 | publisher=[[ISO]] | year=2006 | access-date=2009-10-13 | url-status=live | archive-url=https://web.archive.org/web/20120104072435/http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=43026 | archive-date=2012-01-04 }}</ref><ref name="embedded">{{cite web | title=Audio compression gets better and more complex | url=http://www.embedded.com/design/real-time-and-performance/4025543/Audio-compression-gets-better-and-more-complex | first=Mihir | last=Mody | website=Embedded.com | date=6 June 2005 | access-date=2009-10-13 | url-status=live | archive-url=https://web.archive.org/web/20160208004827/http://www.embedded.com/design/real-time-and-performance/4025543/Audio-compression-gets-better-and-more-complex | archive-date=8 February 2016 }}</ref> The Parametric Stereo audio object type used in HE-AAC v2 was first defined in ISO/IEC 14496-3:2001/Amd 2:2004.<ref name="CT-whitepaper">{{cite web|url=http://www.codingtechnologies.com/products/assets/CT_aacPlus_whitepaper.pdf |title=MPEG-4 aacPlus - Audio coding for today's digital media world|access-date=2007-01-29 |url-status=dead |archive-url=https://web.archive.org/web/20061026031407/http://www.codingtechnologies.com/products/assets/CT_aacPlus_whitepaper.pdf |archive-date=2006-10-26 }}</ref><ref name="parametric">{{cite web | title=Parametric coding for high-quality audio, ISO/IEC 14496-3:2001/Amd 2:2004 | url=http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=39382 | publisher=[[ISO]] | year=2004 | access-date=2009-10-13 | url-status=live | archive-url=https://web.archive.org/web/20120104071002/http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=39382 | archive-date=2012-01-04 }}</ref><ref name="3gpp26401">{{cite web | title=3GPP TS 26.401 V6.0.0 (2004-09), General Audio Codec audio processing functions; Enhanced aacPlus General Audio Codec; General Description (Release 6) | url=http://www.3gpp.org/ftp/Specs/archive/26_series/26.401/26401-600.zip | format=DOC | publisher=3GPP | date=30 September 2004 | access-date=2009-10-13 | url-status=live | archive-url=https://web.archive.org/web/20060819083421/http://www.3gpp.org/ftp/Specs/archive/26_series/26.401/26401-600.zip | archive-date=19 August 2006 }}</ref>

The current version of the AAC standard is defined in ISO/IEC 14496-3:2009.<ref name="mpeg4audio-2009">{{cite web | url=http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=53943 | title=ISO/IEC 14496-3:2009 - Information technology -- Coding of audio-visual objects -- Part 3: Audio | publisher=[[ISO]] | year=2009 | access-date=2009-10-07 | url-status=live | archive-url=https://web.archive.org/web/20110606214516/http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=53943 | archive-date=2011-06-06 }}</ref>

AAC+ v2 is also standardized by [[ETSI]] ([[European Telecommunications Standards Institute]]) as TS 102005.<ref name="CT-whitepaper" />

The [[MPEG-4 Part 3]] standard also contains other ways of compressing sound. These include lossless compression formats, synthetic audio and low bit-rate compression formats generally used for speech.