SACD stands for Super Audio CD, a super audio disc system. It is the latest digital format developed through a collaboration between Sony and Philips, with the potential to fully replace the CD audio source. SACD adopts DSD (Direct Stream Digital) recording technology, which offers both a frequency range and dynamic range superior to that of CDs.
SACD is a new type of optical disc; it does not use the CD format but is more similar to DVD discs, requiring dedicated SACD playback equipment when in use.
The structure of an SACD disc is roughly similar to that of a DVD, with single or double-sided playback surfaces and single or dual-layer information storage. Currently, most SACD discs on the market adopt a single-sided, dual-layer structure: one layer stores traditional 16-bit CD format signals on a 0.6mm substrate, ensuring compatibility with CDs, while the other layer is a high-density, semi-transparent 0.6mm substrate storing SACD format signals. These two substrates are then bonded together in a manner similar to DVD discs. This type of disc can be played on regular CD players as well as on SACD players. Of course, there is a difference in sound quality between the two.