The Future - SACD ?
Future of Audio - SACD
Keeping abreast of sound technology
What is SACD?
Super Audio CD (SACD) is a new development from Sony and Philips, the original creators of the CD. They look the same as ordinary CDs but, thanks to innovative recording and playback techniques, can deliver an amazing richness of sound and unprecedented levels of quality.
How are SACDs recorded?
SACDs are recorded using a process known as Direct Stream Digital (DSD). This samples sound at 2.88224 MHz and stores it as 1 bit data, making it 64 times faster than CDs. This means it can capture a full range of sounds with incredible audio resolution, making it the closest approximation to the original analog waveform available. The upper frequency cut-off extends beyond 100kHz which, when combined with massive noise reduction, allows for an impressive dynamic range of over 120dB across the entire audible range.
DSD can even re-master old analogue master tapes revealing a new level of quality. SACDs are also capable of Multi-Channel audio containing up to 5.1 channels of surround sound.
What does Multi-channel audio mean?
Multi-channel audio allows a more precise reproduction of the acoustic signature of the performance space by recording the sound from different positions within the space onto separate channels, which can then be recreated through an equal number of loudspeakers.
How do SACDs compare to ordinary CDs?
SACDs have the same shape and dimensions as CDs. They differ in recording and playback methods, audio quality, and storage capacity.
CDs are recorded using Pulse Code Modulation (PCM), which allows for a sampling frequency of 44.1kHz encoded at 16-bit resolution. SACDs are recorded via Direct Stream Digital (DSD), which samples at 2.8224MHz encoded as single-bit data, making it 64 times faster.
Playback on CDs has an upper frequency cut-off at just over 22kHz and a dynamic range limit of about 96dB. SACD's cut-off is beyond 100kHz and can deliver a dynamic range of over 120dB across the audible range.
The conventional PCM recording and playback process requires a variety of filters (decimation, interpolation, oversampling and low pass), whereas DSD is far simpler needing only a low pass filter for playback, giving a far more faithful reproduction of the original signal. Ordinary CDs can hold around 650-740MB of data. By contrast, a single layer SACD can hold 7.7GB (over 6 times as much data), and a dual layer disc can store 8.54GB. A single layer SACD can hold over 100 minutes of 2-channel stereo audio (compared to 74 minutes on a CD) as well as multi-channel content.
Will ordinary CDs play on my SACD player?
Yes, a dedicated SACD player can handle all existing CDs.
Will SACDs play on my CD player?
SACDs come in three different types: Single Layer discs (one High Density layer, 4.7GB), Dual Layer discs (two High Density layers, 8.54GB), and Hybrid discs. Hybrid discs are the only ones that will play on an ordinary CD player as they are made up of one High Density layer and one CD layer for complete compatibility.
What 'extras' can SACDs contain?
An extra data area has been reserved on SACD disc which will make it possible to include information in text, graphics and video.
Created: 12th January 2007
Modified: 19th February 2007
