Super Audio CD (SACD) is a high-resolution, read-only optical audio disc format developed by Sony and Philips Electronics, the same companies that created the Compact Disc.
SACD is a disc of identical physical dimensions to a standard compact disc; the density of the disc is the same as a DVD and it encodes audio using a process known as Direct Stream Digital. The SACD sampling rate is 2822.4 kHz and the resolution is one bit. A stereo SACD recording can stream data at an uncompressed rate of 5.6 Mbps; four times higher than the rate for Red Book CD stereo audio. SACD recordings can have a higher frequency response and dynamic range than conventional CDs.
Hybrid Super Audio CDs (which include both a Stereo CD and a Super Audio CD layer) can be played back on CD players. To hear the Super Audio CD Stereo, and on many discs the Super Audio CD Multichannel layer, requires a Super Audio CD player.
SACD audio is stored in a format called Direct Stream Digital (DSD), which differs from the conventional Pulse-code modulation (PCM) used by the compact disc or conventional computer audio systems.
DSD is 1-bit, has a sampling rate of 2.8224MHz, and makes use of noise shaping quantization techniques in order to push 1-bit quantization noise up to inaudible ultrasonic frequencies. This gives the format a greater dynamic range and wider frequency response than the CD. The SACD format is capable of delivering a dynamic range of 120dB from 20Hz to 20kHz and an extended frequency response up to 100kHz, although most currently available players list an upper limit of 70—90kHz, and practical limits reduce this to 50kHz.
