Audio coding format: Difference between revisions

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{{short description|Digitally coded format for audio signals}}

[[File:Opus quality comparison colorblind compatible.svg|thumb|Comparison of coding efficiency between popular audio formats]]

An '''audio coding format'''<ref>The term "audio coding" can be seen in e.g. the name [[Advanced Audio Coding]], and is analogous to the term [[video coding format|video coding]]</ref> (or sometimes '''audio compression format''') is a [[Contentencoded format|content representation format]] for storage or transmission of [[digital audio]], (such as in [[digital television]], [[digital radio]] and in audio and video files). Examples of audio coding formats include [[MP3]], [[Advanced Audio Coding|AAC]], [[Vorbis]], [[FLAC]], and [[Opus (audio format)|Opus]]. A specific software or hardware implementation capable of [[Data_compression#Audio|audio compression]] and decompression to/from a specific audio coding format is called an ''[[audio codec]]''; an example of an audio codec is [[LAME]], which is one of several different codecs which implements encoding and decoding audio in the [[MP3]] audio coding format in software.

Some audio coding formats are documented by a detailed [[technical specification]] document known as an '''audio coding specification'''. Some such specifications are written and approved by [[standardization organization]]s as [[technical standard]]s, and are thus known as an '''audio coding standard'''. The term "standard" is also sometimes used for [[de facto standard|''de facto'' standards]] as well as formal standards.

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[[Perceptual coding]] was first used for [[speech coding]] compression, with [[linear predictive coding]] (LPC).<ref name="Schroeder2014">{{cite book |last1=Schroeder |first1=Manfred R. |title=Acoustics, Information, and Communication: Memorial Volume in Honor of Manfred R. Schroeder |date=2014 |publisher=Springer |isbn=9783319056609 |chapter=Bell Laboratories |page=388 |chapter-url=https://books.google.com/books?id=d9IkBAAAQBAJ&pg=PA388}}</ref> Initial concepts for LPC date back to the work of [[Fumitada Itakura]] ([[Nagoya University]]) and Shuzo Saito ([[Nippon Telegraph and Telephone]]) in 1966.<ref>{{cite journal |last1=Gray |first1=Robert M. |title=A History of Realtime Digital Speech on Packet Networks: Part II of Linear Predictive Coding and the Internet Protocol |journal=Found. Trends Signal Process. |date=2010 |volume=3 |issue=4 |pages=203–303 |doi=10.1561/2000000036 |url=https://ee.stanford.edu/~gray/lpcip.pdf |issn=1932-8346|doi-access=free }}</ref> During the 1970s, [[Bishnu S. Atal]] and [[Manfred R. Schroeder]] at [[Bell Labs]] developed a form of LPC called [[adaptive predictive coding]] (APC), a perceptual coding algorithm that exploited the masking properties of the human ear, followed in the early 1980s with the [[code-excited linear prediction]] (CELP) algorithm which achieved a significant compression ratio for its time.<ref name="Schroeder2014"/> Perceptual coding is used by modern audio compression formats such as [[MP3]]<ref name="Schroeder2014"/> and [[Advanced Audio Codec|AAC]].

[[Discrete cosine transform]] (DCT), developed by [[Nasir Ahmed (engineer)|Nasir Ahmed]], T. Natarajan and [[K. R. Rao]] in 1974,<ref name="DCT">{{cite journal |author1=Nasir Ahmed |author1-link=N. Ahmed |author2=T. Natarajan |author3=Kamisetty Ramamohan Rao |journal=IEEE Transactions on Computers |title=Discrete Cosine Transform |volume=C-23 |issue=1 |pages=90–93 |date=January 1974 |doi=10.1109/T-C.1974.223784 |s2cid=149806273 |url=https://www.ic.tu-berlin.de/fileadmin/fg121/Source-Coding_WS12/selected-readings/Ahmed_et_al.__1974.pdf |access-date=2019-10-20 |archive-date=2016-12-08 |archive-url=https://web.archive.org/web/20161208075733/https://www.ic.tu-berlin.de/fileadmin/fg121/Source-Coding_WS12/selected-readings/Ahmed_et_al.__1974.pdf |url-status=dead }}</ref> provided the basis for the [[modified discrete cosine transform]] (MDCT) used by modern audio compression formats such as MP3<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> and AAC. MDCT was proposed by J. P. Princen, A. W. Johnson and A. B. Bradley in 1987,<ref>{{cite book|doi=10.1109/ICASSP.1987.1169405|chapter-url=https://ieeexplore.ieee.org/document/1169405|chapter=Subband/Transform coding using filter bank designs based on time ___domain aliasing cancellation|title=ICASSP '87. IEEE International Conference on Acoustics, Speech, and Signal Processing|year=1987|last1=Princen|first1=J.|last2=Johnson|first2=A.|last3=Bradley|first3=A.|volume=12|pages=2161–2164|s2cid=58446992}}</ref> following earlier work by Princen and Bradley in 1986.<ref>{{cite journal|doi=10.1109/TASSP.1986.1164954|url=https://ieeexplore.ieee.org/document/1164954|title=Analysis/Synthesis filter bank design based on time ___domain aliasing cancellation|year=1986|last1=Princen|first1=J.|last2=Bradley|first2=A.|journal=IEEE Transactions on Acoustics, Speech, and Signal Processing|volume=34|issue=5|pages=1153–1161|url-access=subscription}}</ref> The MDCT is used by modern audio compression formats such as [[Dolby Digital]],<ref name="Luo">{{cite book |last1=Luo |first1=Fa-Long |title=Mobile Multimedia Broadcasting Standards: Technology and Practice |date=2008 |publisher=[[Springer Science & Business Media]] |isbn=9780387782638 |page=590 |url=https://books.google.com/books?id=l6PovWat8SMC&pg=PA590}}</ref><ref>{{cite journal |last1=Britanak |first1=V. |title=On Properties, Relations, and Simplified Implementation of Filter Banks in the Dolby Digital (Plus) AC-3 Audio Coding Standards |journal=IEEE Transactions on Audio, Speech, and Language Processing |date=2011 |volume=19 |issue=5 |pages=1231–1241 |doi=10.1109/TASL.2010.2087755|bibcode=2011ITASL..19.1231B |s2cid=897622 }}</ref> [[MP3]],<ref name="Guckert"/> and [[Advanced Audio Coding]] (AAC).<ref name=brandenburg>{{cite web|url=http://graphics.ethz.ch/teaching/mmcom12/slides/mp3_and_aac_brandenburg.pdf|title=MP3 and AAC Explained|last=Brandenburg|first=Karlheinz|year=1999|url-status=live|archive-url=https://web.archive.org/web/20170213191747/https://graphics.ethz.ch/teaching/mmcom12/slides/mp3_and_aac_brandenburg.pdf|archive-date=2017-02-13}}</ref>

==List of lossy formats==

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| rowspan="2" | 36–54%{{refn|group=n|name=MarketShareNote|The report combines AC-3 & E-AC-3 and separates [[Dolby Atmos]] from its market share calculation. Dolby Atmos can be encoded either lossily with E-AC-3/[[Dolby AC-4|AC-4]]<ref>{{Cite web |date=2023-05-23 |title=Does Dolby AC-4 support Dolby Atmos? |url=https://professionalsupport.dolby.com/s/article/Does-Dolby-AC-4-support-Dolby-Atmos |access-date=2024-11-08 |website=Dolby Professional Support}}</ref> or losslessly with [[Dolby TrueHD]]. [[Music streaming service|Music]] and [[Video on demand|video streaming]] providers typically use Dolby Digital Plus augmented with Dolby Atmos, whereas [[Music download|digital downloads]] and [[Blu-ray|Blu-ray discs]] typically use Dolby TrueHD augmented with Dolby Atmos.<ref>{{Cite web |date=2023-05-03 |title=Just wait until you hear lossless Dolby Atmos Music |url=https://www.digitaltrends.com/home-theater/lossless-spatial-audio-dolby-atmos-music/ |access-date=2024-11-08 |website=Digital Trends |language=en}}</ref>}}

| rowspan="2" |37–61%{{refn|group=n|name=MarketShareNote}}

| <ref name="Luo" /><ref name="Britanak2011">{{cite journal |last1=Britanak |first1=V. |title=On Properties, Relations, and Simplified Implementation of Filter Banks in the Dolby Digital (Plus) AC-3 Audio Coding Standards |journal=IEEE Transactions on Audio, Speech, and Language Processing |date=2011 |volume=19 |issue=5 |pages=1231–1241 |doi=10.1109/TASL.2010.2087755|bibcode=2011ITASL..19.1231B |s2cid=897622 }}</ref>

|-

|[[Dolby Digital|Dolby Digital Plus]] (E-AC-3)