Super Audio Compact Disc

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'''Super Audio Compact Disc''' ('''SACD''') is a format developed by Sony and Philips to replace their former creation, the [[Compact Disc]]. It competes with [[DVD-Audio]] in that field.

It starts from a fundamentally different approach compared to CD and DVD-Audio, and instead of using [[Pulse Code Modulation|PCM]] for audio data storage, they use another audio data representation technique called [[Pulse-Density Modulation|PDM]] which, according to Philips and Sony claims, is better than PCM.

The main features are:
* Up to 100 kHz bandwidth
* [[Multichannel]]
* 120 dB dynamic range
* Backwards compatible to CD
* Strong encryption
* Meets [[ISC requirements]]

SACD represents a good option for those that want a media that will play everywhere, and not only in the living room SACD player. Discs in this format are often released in two layers (hybrid disc): one is a SACD layer that can only be read by special players, and another is a standard Red Book CD layer that can be read by any CD player.

Still, SACD isn't seeing much success. The likely reason is that users can't be convinced to switch to an expensive technology that doesn't seem to bring them any obvious advantage compared to CD.

The SACD specification is contained in the Scarlet Book, which can be licensed from [Philips]

== References ==
* [ SACD information]

[[Category:Hardware]]

Compact Disc Digital Audio

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'''Compact Disc Digital Audio''' ('''CDDA''') 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 virtually 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 an 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
* 44.1 kHz [[Sampling rate]]
* 16 bit depth

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

There is some error detection and correction 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 are one quarter of the reading laser's wavelength deep so that the reflected laser beam either cancels or amplifies itself when overlayed with its echo, 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. There's also a smaller physical format of only 8 centimeters.

== Succession Candidates? ==
There are some drawbacks to the Audio CD, and various parties have pushed [[DVD-Audio]] and [[Super Audio Compact Disc|SACD]] as replacement for Audio CD.

== References ==
* [Licensing the CD audio technology at Philips]
* [The meaning of each CD book colour]
* [History of the CD]
* [a good resource on compact discs]

[[Category:Hardware]]
[[Category:CD ripping]]

Hydrogenaudio Knowledgebase - User contributions [en]

Super Audio Compact Disc

Compact Disc Digital Audio