Super Audio CD
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Super Audio CD (SACD) is a read-only optical audio disc aimed at providing higher fidelity audio reproduction than the compact disc. Introduced in 1999, it was developed by Sony and Philips, the same companies that created the CD.
SACDs may contain a 2-channel stereo mix, a 5.1 surround sound mix, or both.
There are three types of SACDs:
- Hybrid: Includes an audio CD layer compatible with CD players, and a 4.7GB SACD layer. This is the most popular type.
- Single layer: Similar to a DVD-5 DVD, a 4.7GB SACD layer with no CD layer. This type was used by Sony Music.
- Dual layer: Similar to a DVD-9 DVD, two SACD layers with no CD layer. This type is rarely used.
There is a format war between Super Audio CD and DVD-Audio. Another challenger is the DualDisc format.
At present SACD format has mainly taken the interest of audiophiles, with relatively little mass market acceptance. As of May 2005, there have been approximately 3,000 SACDs releases, about 40% of which are classical music (source: http://www.sa-cd.net). However, some more popular albums have been made as SACDs, including Pink Floyd's album, Dark Side of the Moon.
The Sony Playstation 3, expected in 2006, is set to include SACD support.
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DSD
On SACD, audio is stored in a format called Direct Stream Digital (DSD), which is different than the conventional PCM used by the compact disc. DSD is 1-bit and has a sampling rate of 2,822,400 Hertz. This gives the format a greater dynamic range and wider frequency response than the CD. There is some debate as to whether 1-bit Sigma-delta modulation is better or worse than PCM for high-quality audio. (Audio Engineering Society Convention Paper 5395 (http://sjeng.org/ftp/SACD.pdf))
Copy protection
SACD has copy prevention features at the physical level, which for the moment appear to make this format nearly impossible to perfectly copy. These include 80 bit encryption of the audio data, with a key encoded on a special area of the disk that is only readable by a licensed SACD device. SACD can't be played on a computer, nor can SACDs be created except by a licensed disc replication facility. Copying the music may still be done via an analogue stage (for example, line-out of the SACD player to the line-in of a CD recorder), but doing so is imperfect since the conversion to and from analogue is lossy and the target medium is not capable of storing the music with the fidelity of the source.
See also
External links
da:Super Audio Compact Disc de:Super Audio Compact Disc nl:Super Audio Compact Disc ja:Super Audio CD