SACD Breakthrough 
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Written by Richard Elen   
Friday, 25 August 2000

To date, a major challenge for the Sony/Philips Direct Stream Digital (DSD) one-bit recording system at the heart of Super Audio CD (SACD) concerns the way it has carried out the digital signal processing (DSP) operations that is required for most modern digital recording and mixing, especially multi-track. Until now, this has meant converting the one-bit DSD data stream into something very much akin to the Pulse Code Modulation (PCM) technology it seeks to replace. DSP techniques rely on performing operations on digital words, and if your audio is a single-bit DSD data stream, it won't work.

This, along with the fact that DSD recording requires a whole new set of studio gear, has meant that DSD and SACD have so far been best suited to relatively simple recording chains, in which the signal is captured, recorded, edited and mastered with very little, if any, digital processing. This has limited the system primarily to classical and audiophile recordings - recordings which, on their own, would probably be insufficient to support their own unique recording system.

Now all of that may be about to change. Tom Jung, founder of DMP Records, writes in the August 2000 edition of Pro Audio Review that not one but four separate groups under the Sony banner are working on DSD processing technology that will maintain the integrity of the one-bit, 2.8224 MHz sampling datastream. This can open the way to multi-track DSD recording and mixing, until now the domain of PCM (and analog) multi-track technology.

Field Programmable Gate Array (FPGA) technology is the key, according to Jung, and he notes that Sony has already developed DSD chips. Meanwhile, the Oxford Group in the U.K., led by Peter Easty, is working on EQ, compression, mixing and mastering tools for DSD. At the same time, another group is working on the Sonoma DSD workstation. It looks as though DSD will soon be available to a wider field of recording engineers and projects.

Also of interest in the DSD field is the release of SACD players fitted with DSD digital outputs, such as the Sharp DX-SX1. This development offers several potential benefits, both to consumers and to consumer audio manufacturers.

Until now, digital players offering better than CD quality internally - such as DVD-Video players capable of replaying 24-bit, 96 kHz-sampled discs - have only offered 16-bit, 44.1/48 kHz digital outputs, either in S/PDIF or Dolby/DTS, coax or TOSLink formats. The argument has been that to minimize copyright theft, digital outputs should not exceed "CD quality" without some kind of embedded copy-protection scheme. It is the lack of development of such a scheme that has rendered initial DVD-Audio players devoid of high-density digital outputs and has contributed to delays in the launch of the format (not to be confused with watermarking or on-disc copy-protection issues).

As a result of this decision, there has been no point in consumer audio manufacturers offering receivers or other components that include high-resolution, high-density D/A converters: there has been nothing available to deliver a suitable digital signal to them. For example, if you have a DVD-Video player capable of playing back 24/96 discs, the 24/96 converters are in the player, not in your hi-fi system.

This may be changing with the advent of high-resolution players fitted with high-density digital outputs. No doubt the lead set by Sharp on the SACD front will give DVD manufacturers food for thought. The ability to attach external converters (as well as all-digital amplifiers, like the Sharp SM-SX100, and other components) offer the high-end consumer more choice and possibilities for customization and optimization of a system to suit personal needs. This also means that there is suddenly a market for a lot more gear. Hopefully manufacturers of PCM equipment will take the
hint.








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