Technology
SACD is capable of encoding recorded audio in either stereophonic sound or surround sound. Although SACD audio streams are encoded in a pulse-density modulation (PDM) scheme called Direct Stream Digital (DSD), a manufacturer may also write a Pulse-code modulation (PCM) "layer" compatible with conventional Compact Disc players.
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 2.8224 MHz and the resolution is one bit. A stereo SACD recording can stream data at an uncompressed rate of 5.6 Mbit/s, four times the rate for Red Book CD stereo audio. SACD recordings can have a wider frequency and dynamic range than conventional CDs.
| CD | SACD | |
|---|---|---|
| Format | 16 bit PCM | 1 bit DSD |
| Sampling frequency | 44.1 kHz | 2.8224 MHz |
| Dynamic range | 90 dB (practical) 96 dB (theoretical) |
105 dB (practical) 120 dB (theoretical) |
| Frequency range | 20 Hz – 20 kHz | 20 Hz – 50 kHz (practical) 2 Hz – 100 kHz (theoretical) |
| Disc capacity | 700 MB | 4.7 GB |
| Stereo | Yes | Yes |
| Discrete surround | Never implemented | Yes |
There are three types of SACDs:
- Hybrid: Hybrid SACDs are encoded with a 4.7 GB DSD layer (also known as the HD layer), as well as a PCM (Red Book) audio layer readable by most conventional Compact Disc players.
- Single-layer: A DVD-5 encoded with one 4.7 GB DSD layer. Single-layer SACDs are not backward-compatible with conventional CD players.
- Dual-layer: A DVD-9 encoded with two DSD layers, totaling 8.5 GB, and no PCM layer. Dual-layer SACDs can store nearly twice as much data as a single-layer SACD. Like single-layer SACDs, dual-layer discs are not backward-compatible with conventional CD players.
Almost all commercially released SACDs have included both stereo (dual-channel) and surround sound (multi-channel) mixes. A multi-channel mix need not be surround, however; some of the Living Stereo reissues (such as the RCA reissue of the 1957 Chicago Symphony Orchestra recording of Mussorgsky's Pictures at an Exhibition) use only the three front channels to reproduce the original three-track (3.0) stereo recordings. Nor is a surround mix obliged to use all six SACD channels (five full-range plus LFE). For example, the 2001 SACD release of Mike Oldfield's Tubular Bells remains in the quadraphonic 4.0 mix.
The CD layer exists primarily for backward compatibility, but is not required. If the CD layer is omitted, the SACD need not be limited to an 80-minute playing time. For stereo material, the space that would have been taken by the multi-channel program can be used to extend playing time to four hours or more. BIS has taken advantage of this to put all of Bach's organ music on five SACD-only disks.
Read more about this topic: Super Audio CD
Famous quotes containing the word technology:
“Radio put technology into storytelling and made it sick. TV killed it. Then you were locked into somebody else’s sighting of that story. You no longer had the benefit of making that picture for yourself, using your imagination. Storytelling brings back that humanness that we have lost with TV. You talk to children and they don’t hear you. They are television addicts. Mamas bring them home from the hospital and drag them up in front of the set and the great stare-out begins.”
—Jackie Torrence (b. 1944)
“The real accomplishment of modern science and technology consists in taking ordinary men, informing them narrowly and deeply and then, through appropriate organization, arranging to have their knowledge combined with that of other specialized but equally ordinary men. This dispenses with the need for genius. The resulting performance, though less inspiring, is far more predictable.”
—John Kenneth Galbraith (b. 1908)
“If we had a reliable way to label our toys good and bad, it would be easy to regulate technology wisely. But we can rarely see far enough ahead to know which road leads to damnation. Whoever concerns himself with big technology, either to push it forward or to stop it, is gambling in human lives.”
—Freeman Dyson (b. 1923)