SACD and DSD Explained
SACD:
SACD is the new release format being developed by Sony and Philips using modern optical disc storage technology. The disc has two data layers. One layer uses the high-density medium found in DVD to hold up to 6 tracks of DSD audio plus text information identifying the disc and its tracks. The second layer is a standard "Red Book" CD layer containing the same program which can be played in any standard CD player.
DSD:
DSD is the new digital recording technology employed by the SACD. A high-density format dependent on the high speed microprocessors and large capacity storage devices being created by the modern high tech boom, DSD takes a new approach to the basic problems of digital music recording. By using a completely different system of encoding, DSD avoids many of the limitations of physics, electronics, and manufacturing technology inherent to the current method of PCM recording used for CDs and other current digital audio applications.
The encoding process uses a single bit (1 or 0) to represent how the music signal (acoustic or electronic waveform) is changing over time, that is, taking its trajectory rather than its absolute value. This process is repeated very rapidly--2.8 million times per second--to get an accurate picture of how the signal is shaped. Such a high sample rate (2.8MHz) allows the system to record frequencies far beyond the scope of human hearing, with a theoretical limit almost 70 times that of CD-quality PCM. Moreover, it eliminates the need for analog components of the A to D converter design which are very difficult to build and can have dramatic effect on the overall audio quality of the device.
PCM systems have a dynamic range and signal resolution fixed by the length of the digital word. The number of bits allocated to each sample (16 bits per sample; 44,100 samples/sec for CD) determines the number of increments of amplitude we can divide the music signal into. DSD systems only consider the change in amplitude from sample to sample (1 bit; 2.8 million samples per second). Thus, they can record the signal in any number of relative steps rather than having to determine which of a fixed number of amplitude values best describes the signal at any given sample point. This higher resolution can lead to a more accurate and musical reproduction of the original sound.