|
Back To Articles Main Page
DSD Recording Format Sets New Professional Standard
By John Kellogg, General Manager, Multichannel Audio and Music Production, Dolby Laboratories
Overcoming the limitations of PCM
The last two decades have seen many advances in professional recording capabilities. So much so that transferring today's top-quality digital studio recordings onto CD using the traditional PCM format actually reduces audio quality. The PCM format was the best available when the CD was developed, but it is limited by its dependence on decimation digital filters, a 44.1 kHz sampling frequency and 16 bit quantization. The DVD recording format does not have these limitations.
Remaining faithful to the original
The Super Audio CD uses the DSD format. Thanks to it's 2.8224MHz sampling frequency for the original 1-bit data, DSD allows direct recording of a Super Audio CD master. Superfluous quantization and decimation processes are eliminated, and the pulse remains exceptionally faithful to the original. And with DSD for playback, there's no need for interpolation and steep anti-aliasing filters to block frequencies above 20 kHz. Consequently, the frequency response is broadened to 100 kHz with a dynamic audible frequency range of 129dB. DSD allows direct recording of a very accurate pulse, which can be played back with ease for exceptional results.
The only media for high fidelity pure audio
This presents a double-edged opportunity for the music industry. The DSD format and Super Audio CD not only allows for production of exceptionally high-quality audio masters for new titles, but is excellent for preserving existing analog recording archives. Super Audio CD is the ideal media for recording and playback of high fidelity pure audio.
Direct Stream Digital eliminates the need for these filters, enabling sound to be recorded directly in the original 1-bit signal format.
Direct Stream Digital eliminates the need for these filters, enabling sound to be recorded directly in the original 1-bit signal format.
The above diagram demonstrates the high fidelity of DSD recording. The 10 kHz square wave frequency (top line in the diagram) includes high-frequency components which clearly exceed the audio range. With the 16-bit PCM system, these are converted into 10 kHz sine waves (left diagram). However, with the 1-bit DSD system, the reproduced sound wave is nearly identical to the original sound wave (right diagram).
Three disc variations - all with remarkable performance
Six times as much information
Super Audio CD discs are the same size and thickness as conventional CD discs, yet they can store about six times as much information - all on a single layer. This means a lot more high-quality, high-volume audio data. Super Audio CD format has space for 2-channel stereo recordings, multichannel recordings and a separate area for graphics or text such as song lyrics and liner notes.
Hybrid Super Audio CD discs
 In addition to single and dual type discs that store high volume audio data, hybrid Super Audio CD discs are also available. These have an extra CD layer beneath the semi transparent HD layer to allow them to be played on conventional CD player. The different wavelength and aperture of a conventional CD player's pickup laser makes it possible to read the CD data through the HD layer. And provided the CD layer was produced using Super Bit Mapping Direct (SBM Direct) technology, DSD format data can be accurately down converted for higher quality playback fro the CD layer.
Back To Articles Main Page
|
