By Derk Reefman, peter nuijten, philips research laboratories                                      

n this paper, an overview of DSD signal processing is given. It is shown that 1-bit DSD signals can be dithered properly. Here, properly means that the resulting dithered DSD stream does not contain audible artifacts in a band from 0-100 kHz. It is also shown that signal processing can be done best in a high rate, multi-bit domain. The minimal frequency span needed to comply with the human auditory system appears to be roughly 0-350 kHz (»8.1 kHz). Following the signal processing, final conversion to DSD is made. We make a plea for SACD as a consumer format; it is the format which, while maintaining all necessary psycho-acoustical characteristics such as high bandwidth, filtering with wide transition bands etc., uses the least bits from the disk; hence offering the longest playing time.

In the past few years, there has been an evolving trend in the audio world to move from the standard CD-format (i.e., 16 bit resolution, and a sampling frequency of 44.1 kHz) to other formats, which offer a higher resolution. A nice description of this otherwise rather vague definition is given by the AES high-resolution audio technical committee: every carrier offering more than 2 channels, each 44.1 or 48 kHz and resolution corresponding to 16 bit, is coined as high-resolution. Hence, high resolution embraces both multi-channel recordings and audio formats which allow for a higher definition of the audio data per sé, such as SACD, which stores 1-bit words at a sampling frequency of 64 times 44.1 kHz, and DVD-A, which covers a wide variety of sampling rates (44.1/48 to 176/192 kHz) and wordlengths (16-24 bit). Often, the SACD data format is called bitstream or Direct Stream Digital (DSD) to contrast it with the Pulse Code modulation (PCM) used in the

Multichannel high-density audio format
Does DSD (bitstream) have 
the right equation?
SACD or DVD-Audio? Players of both formats are already available to choose from! At this years AES in May, Philips Research Laboratories is presenting this article as a paper on the DSD audio format (SACD). Does this basic technology question, Bitstream or PCM concern the replication industry? Have format, will replicate! is the credo of replicators. Right? But then, this basic technology is responsible for the format war.
Optical Disc Systems is glad in featuring the paper in toto. In the last issue the argument against bitstream was featured. A comparison is now made possible with this article. Sony and Philips have the authoring tools for SACD in place.
To provide a broader perspective on DSD recording in the studio, a complimentary article ‘SACD Format: Development of the DSD recording solution’, is included in this issue.
Finally, the real-politik is not only about technology. Format synergy, user friendliness, practicality will ultimately decide which disc will replicate.
In the ODS’ next issue we provide an article on SACD-Authoring and Editing.

JANUARY -FEBRUARY 2001                                  OPTICAL DISC SYSTEMS         Back to content    Back to Magazine Cover

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