SACD
The technology that the SACD uses to digitally encode audio signals is quite different from that used in the CD and DVD-Audio. It uses a 1-bit delta-sigma modulation process known as Direct Stream Digital and it works at the very high sampling rate of 2.8224 MHz per second. This is 64 times the sampling rate used in Compact Disc Digital Audio.
SACD has multi-channel surround sound feature. The label located at the back cover bears either the words "SACD Surround" or its own "Multi-Ch" logo.
There are three types of SACDs. The first type is a Hybrid SACD. It is the most popular of the three versions. The Hybrid type includes a "Red Book" layer which can synchronize with the existing Compact Disc players. This layer is called the ‘CD layer’. The other SACD layer, called the ‘HD layer’, has a storage capacity of 4.7 gigabytes.
The second type of SACD has a single layer. It can be physically characterized as a single-layer DVD-5 DVD. This layer contains a 4.7 gigabyte HD layer. There is no provision of any CD layer in it.
The third type of SACD has a double layer. It has the physical features of a DVD-9 DVD. Its double layer contains two HD layers with a total storage capacity of 8.5 gigabytes.
Both Philips and Sony launched SACD formats in 1999/2,000 and based them on direct stream digital coding. They used modern optical disc storage technology to produce SACDs. An SACD has two data layers. One layer utilizes the high density medium which a DVD has to store up to six tracks of DSD audio and text signals which identify the disc and its tracks. The second layer of the SACD is a standard ‘red book’ CD layer which contains the same program that can be played in any standard CD player.
A fierce competition is going on between the SACD and the DVD-Audio in respect of their formats with no clear cut results showing general public acceptance of one format over the other. SACDs, however, appear to have an edge over the DVD-Audio in the sense that most SACD discs have hybrid designs which are compatible with the existing CD players. A common man likes a media player that can play multiple formats including SACD and DVD-Audio which are cheaply available.
