Compact Disc Digital Audio

2005-02-02T03:49:57Z

221.153.157.92:

=Introduction=

CDDA - Compact Disc Digital Audio - is surely the most popular audio recording delivery media these days. The media itself is cheap, quality is very good, it's easy to use and it's playable everywhere.

==History==

The CD format was developed as a joint cooperation between [http://www.sony.com Sony] and [http://www.philips.com Philips] in the late seventies, and was released by them as the [[Red Book]] standard in the eighties.

It was an instant success. It was introduced in the United States in 1983, and in the same year 30,000 players and 800,000 discs were sold. In 1986, the numbers raised to 3 million players and 53 million discs. In early nineties, players were selling at a rate of 9.2 million units each year, and at the same period of time and average of 288 million discs left store shelves.

Since the format was so amazingly successful, Sony and Philips got together again in 1987 to standardize Video CD (White Book). Later on, they would still cooperate in developing CD-ROM and CD-ROM XA (Yellow Book), Enhanced CD/CD Extra (Blue Book) and CD-R/CD-RW (Orange Book).

==Specifications==

[[PCM]] audio is usually pressed on CD with the following characteristics:

* [[Stereo]] sound
* 44.1kHz [[Sampling rate]]
* 16 bit depth

There are also provisions in the standard for quadraphonic audio (4 channels, 22.05kHz sampling rate), but it's very rarely used.

There is some error correction and detection code in CDDA. It's called C1 and C2 information, and is based on Reed-Solomon algorithms.

The data in a CD starts in the inside of the disc and is read in a spiral towards the outer edge. The standard defines that a CD can contain 74 minutes of audio (rumour has it that this number was decided so that Beethoven's 9th symphony would fit inside a CD). Later, manufacturers managed to push that limit to 80 minutes.

A CD is a disc of polycarbonate with a reflective layer. Pressed CDs have pits that either deflect the laser or let it pass through to the reflective layer, that way generating a binary method to store information. In the case of a CD-R, it contains a pigment that is burned by the writing laser so that the reading laser will deflect when hitting it. Parts not burned will let the laser pass through to the reflective layer.

A CD has a diameter of 12 centimeters / 4.7 inches.

==Links==

See also: candidates to CD succession: [[DVD-Audio]] and [[SACD]]

[http://www.licensing.philips.com/information/cd/audio/ Licensing the CD audio technology at Philips]

[http://www.disctronics.co.uk/technology/cdbasics/cd_books.htm The meaning of each CD book colour]

[http://www.oneoffcd.com/info/historycd.cfm History of the CD]

[http://www.cd-rw.org/ CD-rw.org, a good resource on compact discs]

Windows Media Audio

2005-01-01T03:01:07Z

221.153.157.92:

'''Windows Media Audio''' ([[WMA]]) is a proprietary compressed audio file format used by Microsoft. It was initially a competitor to the [[MP3]] format, but with the introduction of Apple's [[iTunes]] Music Store, it has positioned itself as a competitor to the [[advanced audio coding]] format used by Apple. It is part of the Windows Media framework. An initial reason for the development of WMA might have been that [[MP3]] technology is patented and has to be licensed from Thomson for inclusion in the Microsoft Windows operating system.However Windows Media Player 10 for Windows XP now also includes MP3 encoding as an option for CD ripping.

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Compact Disc Digital Audio

Windows Media Audio