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The first commercially available audio [[CD player]], the [[Sony CDP-101]], was released in October 1982 in Japan. The format gained worldwide acceptance in 1983–84, selling more than a million CD players in its first two years, to play 22.5 million discs,<ref>{{cite book |last=Pohlmann |first=Ken C. |title=Principles of Digital Audio |date=2000 |publisher=McGraw-Hill |isbn=978-0-07-134819-5 |page=244}}</ref> before overtaking [[phonograph record|records]] and [[Cassette tape|cassette tapes]] to become the dominant standard for commercial music. Peaking around year 2000, the audio CD contracted over the next decade due to rising popularity and revenue from [[Music download|digital downloading]], and during the 2010s by [[Music streaming service|digital music streaming]],<ref>{{cite news |date=14 April 2015 |title=IFPI publishes Digital Music Report 2015 |url=https://www.ifpi.org/news/Global-digital-music-revenues-match-physical-format-sales-for-first-time |url-status=live |archive-url=https://web.archive.org/web/20150414194629/https://www.ifpi.org/news/Global-digital-music-revenues-match-physical-format-sales-for-first-time |archive-date=14 April 2015 |access-date=1 July 2016}}</ref> but has remained as one of the primary distribution methods for the [[music industry]].<ref name="AutoMR-2">{{cite news |last=Plambeck |first=Joseph |date=30 May 2010 |title=As CD Sales Wane, Music Retailers Diversify |url=https://www.nytimes.com/2010/05/31/business/media/31bestbuy.html |url-status=live |archive-url=https://web.archive.org/web/20170501175846/https://www.nytimes.com/2010/05/31/business/media/31bestbuy.html |archive-date=1 May 2017 |work=The New York Times}}</ref> In the United States, phonograph record revenues surpassed the CD in 2020 for the first time since the 1980s,<ref>{{cite news |date=10 September 2020 |title=Vinyl Outsells CDs For the First Time in Decades |url=https://pitchfork.com/news/vinyl-outsells-cds-for-the-first-time-in-decades/ |url-status=live |archive-url=https://archive.today/20200922170131/https://pitchfork.com/news/vinyl-outsells-cds-for-the-first-time-in-decades/amp/ |archive-date=22 September 2020 |access-date=22 September 2020}}</ref><ref>{{cite web |title=Mid-Year 2020 RIAA Revenue Statistics |url=https://www.riaa.com/wp-content/uploads/2020/09/Mid-Year-2020-RIAA-Revenue-Statistics.pdf |url-status=live |archive-url=https://web.archive.org/web/20230509100235/https://www.riaa.com/wp-content/uploads/2020/09/Mid-Year-2020-RIAA-Revenue-Statistics.pdf |archive-date=9 May 2023 |access-date=2 June 2023 |website=Riaa.com}}</ref> but in other major markets like Japan it remains the premier music format by a distance<ref>{{Cite web |date=2023-10-23 |title=3 observations on… how Japan's music industry caters to (and relies on) 'superfans' more than any other market |url=https://www.musicbusinessworldwide.com/3-observations-on-how-japans-music-industry-caters-to-and-relies-on-superfans-more-than-any-other-market1/ |access-date=2024-05-03 |website=Music Business Worldwide |language=en-US}}</ref> and in Germany it outsold other physical formats at least fourfold in 2022.<ref>{{Cite web |title=Statistik {{!}} Absatz von physischen Tonträgern und digitalen Musikprodukten |url=https://miz.org/de/statistiken/absatz-von-physischen-tontraegern-und-digitalen-musikprodukten |access-date=2024-05-03 |website=miz.org |language=de}}</ref>
In the music industry, audio CDs have been generally sold as either a [[CD single]] (now largely dormant), or as full-length [[album]]s, the latter of which has been more commonplace since the 2000s.<ref>{{Cite web |title=1999: The Year the Record Industry Lost Control |url=https://theafterword.co.uk/1999-the-year-the-record-industry-lost-control/ |access-date=2024-05-03 |website=theafterword.co.uk}}</ref> The format has also been influential in the progression of [[video game music]], used in [[Mixed Mode CD|mixed mode]] [[CD-ROM|CD-ROMs]], providing CD-quality audio popularized during the 1990s on hardware such as [[PlayStation (console)|PlayStation]], [[Sega Saturn]] and [[personal
== History ==
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CDs continued to be strong in some markets such as Japan where 132 million units were produced in 2019.<ref>{{Cite web|url=https://www.nippon.com/en/japan-data/h00740/|title=Physical Formats Still Dominate Japanese Music Market|date=24 June 2020|website=nippon.com|access-date=14 November 2022|archive-date=28 October 2022|archive-url=https://web.archive.org/web/20221028183640/https://www.nippon.com/en/japan-data/h00740/|url-status=live}}</ref>
The decline in CD sales has slowed in recent years; in 2021, CD sales increased in the US for the first time since 2004,<ref>{{cite web | url=https://www.strata-gee.com/lets-get-physical-vinyl-sales-up-51-cd-sales-up-for-first-time-in-17-yrs/ | title=Let's Get Physical! Vinyl Sales up >51%, CD Sales up for First Time in 17-yrs | website=Strata-gee.com | date=26 January 2022 | access-date=14 November 2022 | archive-date=14 November 2022 | archive-url=https://web.archive.org/web/20221114140242/https://www.strata-gee.com/lets-get-physical-vinyl-sales-up-51-cd-sales-up-for-first-time-in-17-yrs/ | url-status=live }}</ref> with [[Axios (website)|Axios]] citing its rise to "young people who are finding they like hard copies of music in the digital age".<ref>{{Cite web|url=https://www.makeuseof.com/cd-sales-are-rising-again-but-why/|title=CD Sales Are Rising Again, but Why?|first=Patrick|last=Kariuki|date=18 March 2022|website=Makeuseof.com|access-date=14 November 2022|archive-date=27 August 2023|archive-url=https://web.archive.org/web/20230827104056/https://www.makeuseof.com/cd-sales-are-rising-again-but-why/|url-status=live}}</ref> It came at the same time as both vinyl and cassette reached sales levels not seen in 30 years.<ref>{{Cite web|url=https://www.officialcharts.com/chart-news/vinyl-and-cassette-uk-sales-continue-to-surge-to-30-year-high-as-cd-sales-decline-slows__34839/|title=Vinyl and cassette UK sales continue to surge to 30 year high|website=Officialcharts.com|access-date=14 November 2022|archive-date=27 August 2023|archive-url=https://web.archive.org/web/20230827104058/https://www.officialcharts.com/chart-news/vinyl-and-cassette-uk-sales-continue-to-surge-to-30-year-high-as-cd-sales-decline-slows__34839/|url-status=live}}</ref> The [[Recording Industry Association of America|RIAA]] reported that CD revenue made a dip in 2022, before increasing again in 2023 and overtook downloading for the first time in over a decade.<ref>{{cite report |last=Bass |first=Matthew |date=2024 |title=Year-end 2023 RIAA Revenue Statistics |url=https://www.riaa.com/wp-content/uploads/2024/03/2023-Year-End-Revenue-Statistics.pdf
In the US, 33.4 million CD albums were sold in the year 2022.<ref>{{Cite web |title=Physical album shipments in the U.S. 2022 |url=https://www.statista.com/statistics/186772/album-shipments-in-the-us-music-industry-since-1999/ |access-date=2024-05-03 |website=Statista |language=en}}</ref> In [[France]] in 2023, 10.5 million CDs were sold, almost double that of vinyl, but both of them represented generated 12% each of the French music industry revenues.<ref>{{Cite web |last=Bazoge |first=Mickaël |date=2024-03-27 |title=En France comme aux États-Unis, les vinyles en position de force face aux CD |url=https://www.01net.com/actualites/en-france-comme-aux-etats-unis-les-vinyles-en-position-de-force-face-aux-cd.html |access-date=2024-05-03 |website=01net.com |language=fr-FR}}</ref>
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There was a long debate over the use of 16-bit (Sony) or 14-bit (Philips) [[Quantization (signal processing)|quantization]], and 44,056 or 44,100 samples/s (Sony) or approximately 44,000 samples/s (Philips). When the Sony/Philips task force designed the Compact Disc, Philips had already developed a 14-bit [[D/A converter]] (DAC), but Sony insisted on 16-bit. In the end Sony won, so 16 bits and 44.1 kilosamples per second prevailed. Philips found a way to produce 16-bit quality using its 14-bit DAC by using four times [[oversampling]].<ref name=Immink />
Some early CDs were mastered with [[pre-emphasis]], an artificial boost of high audio frequencies. The pre-emphasis improves the apparent signal-to-noise ratio by making better use of the channel's dynamic range. On playback, the player applies a de-emphasis filter to restore the frequency response curve to an overall flat one. Pre-emphasis time constants are 50 μs and 15 μs (9.49 dB boost at 20 kHz), and a binary flag in the disc [[subcode]] instructs the player to apply de-emphasis filtering if appropriate. Playback of such discs in a computer or [[CD ripper|ripping]] to [[WAV]] files typically does not take into account the pre-emphasis, so such files play back with an incorrect frequency response.{{citation needed|date=January 2022}} [[FFmpeg]] has a filter to remove (or apply) the pre-emphasis in order to create standard WAV files, or to create CDs with pre-emphasis.<ref>{{cite web |title=FFmpeg Filters Documentation |url=https://ffmpeg.org/ffmpeg-filters.html#aemphasis |website=FFmpeg |publisher=FFmpeg project |access-date=6 January 2024 |archive-date=28 March 2017 |archive-url=https://web.archive.org/web/20170328021020/https://ffmpeg.org/ffmpeg-filters.html#aemphasis |url-status=live }}</ref>
Four-channel, or [[quadraphonic]], support was originally intended to be included in CD-DA.<ref>{{Cite book|url = https://books.google.com/books?id=jqwgBQAAQBAJ&q=Four-channel+Compact+Disc+Digital+Audio&pg=PA108|title = Digital Audio and Compact Disc Technology|isbn = 978-1-4831-4039-1|last1 = Baert|first1 = Luc|last2 = Theunissen|first2 = Luc|last3 = Vergult|first3 = Guido|date = 2013-10-22| publisher=Newnes |access-date = 27 August 2023|archive-date = 27 August 2023|archive-url = https://web.archive.org/web/20230827104057/https://books.google.com/books?id=jqwgBQAAQBAJ&q=Four-channel+Compact+Disc+Digital+Audio&pg=PA108|url-status = live}}</ref> The ''Red Book'' specification briefly mentioned a four-channel mode in its June 1980,<ref name="RedBook1980">"Red Book" Audio CD specification, June 1980, Sony/Philips</ref> September 1983,<ref name="RedBook1983">"Red Book" Audio CD specification, September 1983, Sony/Philips</ref> and November 1991<ref name="RedBook1991">"Red Book" Audio CD specification, November 1991, Sony/Philips</ref> editions. On the first page, it lays out the "Main parameters" of the CD system, including: "Number of channels: 2 and/or 4 simultaneously[*] sampled." The footnote says, "In the case of more than two channels the encoder and decoder diagrams have to be adapted."
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Unlike on a [[DVD]] or CD-ROM, there are no [[computer file|files]] on a ''Red Book'' audio CD; there is only one continuous stream of [[LPCM]] audio data, and a parallel, smaller set of 8 [[subcode]] data streams. Computer [[operating system]]s, however, may provide access to an audio CD as if it contains files. For example, [[Windows]] represents the CD's table of contents as a set of [[Compact Disc Audio track]] (CDA) files, each file containing indexing information, not audio data. By contrast however, [[Finder (software)|Finder]] on [[macOS]] presents the CD's content as an actual set of files, with the [[Audio Interchange File Format|AIFF]]-extension, which can be copied directly, randomly and individually by track as if it were actual files. In reality, macOS performs rips as needed in the background, transparent to the user. The copied tracks are fully playable and editable on the user's computer.
In a process called [[CD ripper|ripping]], digital audio extraction software can be used to read CD-DA audio data and store it in files. Common [[audio file format]]s for this purpose include WAV and AIFF, which simply preface the LPCM data with a short [[header (computing)|header]]; [[FLAC]], [[Apple Lossless|ALAC]], and [[Windows Media Audio Lossless]], which compress the LPCM data in ways that conserve space yet allow it to be restored without any changes; and various [[lossy]], [[perceptual audio coder|perceptual coding]] formats like [[MP3]], [[Advanced Audio Coding|AAC]], and [[Opus (audio format)|Opus]], compress the audio data to a greater degree in ways that irreversibly change the audio, but that exploit features of human hearing to make the changes difficult to discern.
== Format variations ==
Recording publishers have created CDs that violate the ''Red Book'' standard. Some do so for the purpose of [[copy
[[Super Audio CD]] was a standard published in 1999 that aimed to provide better audio quality than CDs. [[DVD-Audio]] emerged at around the same time.<ref name="Auto45-12" /> Both formats were designed to feature audio of higher fidelity by using a higher sampling rate and [[DVD]] media. Neither format was widely accepted.
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