Editing Advanced Audio Coding (section)

===Background===
The [[discrete cosine transform]] (DCT), a type of [[transform coding]] for [[lossy compression]], was proposed by [[N. Ahmed|Nasir Ahmed]] in 1972, and developed by Ahmed with T. Natarajan and [[K. R. Rao]] in 1973, publishing their results in 1974.<ref name="Ahmed">{{cite journal |last=Ahmed |first=Nasir |author-link=N. Ahmed |title=How I Came Up With the Discrete Cosine Transform |journal=[[Digital Signal Processing (journal)|Digital Signal Processing]] |date=January 1991 |volume=1 |issue=1 |pages=4–5 |doi=10.1016/1051-2004(91)90086-Z |bibcode=1991DSP.....1....4A |url=https://www.scribd.com/doc/52879771/DCT-History-How-I-Came-Up-with-the-Discrete-Cosine-Transform|url-access=subscription }}</ref><ref name="pubDCT">{{Citation |first1=Nasir |last1=Ahmed |author1-link=N. Ahmed |first2=T. |last2=Natarajan |first3=K. R. |last3=Rao |title=Discrete Cosine Transform |journal=IEEE Transactions on Computers |date=January 1974 |volume=C-23 |issue=1 |pages=90–93 |doi=10.1109/T-C.1974.223784|s2cid=149806273 }}</ref><ref name="pubRaoYip">{{Citation |last1=Rao |first1=K. R. |author-link1=K. R. Rao |last2=Yip |first2=P. |title=Discrete Cosine Transform: Algorithms, Advantages, Applications |publisher=Academic Press |location=Boston |year=1990 |isbn=978-0-12-580203-1}}</ref> This led to the development of the [[modified discrete cosine transform]] (MDCT), proposed by J. P. Princen, A. W. Johnson and A. B. Bradley in 1987,<ref>J. P. Princen, A. W. Johnson und A. B. Bradley: ''Subband/transform coding using filter bank designs based on time domain aliasing cancellation'', IEEE Proc. Intl. Conference on Acoustics, Speech, and Signal Processing (ICASSP), 2161–2164, 1987</ref> following earlier work by Princen and Bradley in 1986.<ref>John P. Princen, Alan B. Bradley: ''Analysis/synthesis filter bank design based on time domain aliasing cancellation'', IEEE Trans. Acoust. Speech Signal Processing, ''ASSP-34'' (5), 1153–1161, 1986</ref> The [[MP3]] [[audio coding standard]] introduced in 1992 used a hybrid coding algorithm that is part MDCT and part [[FFT]].<ref name="Guckert">{{cite web |last1=Guckert |first1=John |title=The Use of FFT and MDCT in MP3 Audio Compression |url=http://www.math.utah.edu/~gustafso/s2012/2270/web-projects/Guckert-audio-compression-svd-mdct-MP3.pdf |website=[[University of Utah]] |date=Spring 2012 |access-date=14 July 2019}}</ref> AAC uses a purely MDCT algorithm, giving it higher compression efficiency than MP3.<ref name="brandenburg"/> Development further advanced when [[Lars Liljeryd]] introduced a method that radically shrank the amount of information needed to store the digitized form of a song or speech.<ref>{{Cite web |last=Borland |first=John |date=March 18, 2004 |title=The sound of science |url=https://www.cnet.com/tech/services-and-software/the-sound-of-science/ |access-date=2023-04-21 |website=CNET |language=en}}</ref>

AAC was developed with the cooperation between [[AT&T Labs]], [[Dolby]], [[Fraunhofer Society|Fraunhofer IIS]] (who developed MP3) and [[Sony|Sony Corporation]].<ref name=":3" /> AAC was officially declared an international standard by the [[Moving Picture Experts Group]] in April 1997. It is specified both as ''Part 7 of the MPEG-2 standard'', and ''Subpart 4 in Part 3 of the MPEG-4 standard''.<ref name="mpeg4audio-version4-2009">{{Cite tech report |url=http://webstore.iec.ch/preview/info_isoiec14496-3%7Bed4.0%7Den.pdf |title=ISO/IEC 14496-3:2009 - Information technology -- Coding of audio-visual objects -- Part 3: Audio |date=1 September 2009 |access-date=2009-10-07 |archive-url=https://web.archive.org/web/20110614010613/http://webstore.iec.ch/preview/info_isoiec14496-3%7Bed4.0%7Den.pdf |url-status=live |archive-date=14 June 2011 |publisher=[[ISO]]/[[IEC]]}}</ref> Further companies have contributed to development in later years including [[Bell Labs]], [[LG Electronics]], [[NEC]], [[Nokia]], [[Panasonic]], [[ETRI]], [[JVC Kenwood]], [[Philips]], [[Microsoft]], and [[Nippon Telegraph and Telephone|NTT]].<ref name="aac-licensors">{{cite web |title=AAC Licensors |url=https://www.via-corp.com/licensing/aac/aac-licensors/ |access-date=15 January 2020 |website=Via Corp}}</ref><ref name="businesswire">{{cite web |date=5 January 2009 |title=Via Licensing Announces Updated AAC Joint Patent License |url=https://www.businesswire.com/news/home/20090105005026/en/Licensing-Announces-Updated-AAC-Joint-Patent-License |access-date=18 June 2019 |website=[[Business Wire]]}}</ref>