"Why 1-Bit Sigma-Delta Conversion is Unsuitable for High-Quality Applications" - Stanley P. Lipshitz & John Vanderkooy
Single-stage, 1-bit sigma-delta converters are in principle imperfectible. We prove this fact. The reason, simply stated, is that, when properly dithered, they are in constant overload. Prevention of overload allows only partial dithering to be performed. The consequence is that distortion, limit cycles, instability, and noise modulation can never be totally avoided. We demonstrate these effects, and using coherent averaging techniques, are able to display the consequent profusion of nonlinear artifacts which are usually hidden in the noise floor. Recording, editing, storage, or conversion systems using single-stage, 1-bit sigma-delta modulators, are thus inimical to audio of the highest quality. In contrast, multi-bit sigma-delta converters, which output linear PCM code, are in principle infinitely perfectible. (Here, multi-bit refers to at least two bits in the converter.) They can be properly dithered so as to guarantee the absence of all distortion, limit cycles, and noise modulation. The audio industry is misguided if it adopts 1-bit sigma-delta conversion as the basis for any high-quality processing, archiving, or distribution format to replace multi-bit, linear PCM.
(AES Paper 5395)
"Why Direct Stream Digital (DSD) is the Best Choice as a Digital Audio Format" - Derk Reefman & Peter Nuijten
In this paper, an overview of Direct Stream Digital (DSD) signal processing is given. It is shown that 1-bit DSD signals can be dithered properly, so the resulting dithered DSD stream does not contain audible artifacts in a band from 0-100kHz. It is also shown that signal processing can be done best in a high rate, multi-bit domain. Arguments are given that the minimal frequency span needed to comply with the human auditory system is roughly 0-300kHz. Following the signal processing, final conversion to DSD is made. It is demonstrated that Super Audio CD (SACD) is a very efficient consumer format: it is the format which, while maintaining all necessary psycho-acoustical characteristics such as high band width, filtering with wide transition bands etc, uses the least bits from the disk; hence offering the longest playing time.
(AES Paper 5396)
"SDM versus LPCM: the debate continues" - M.O.J. Hawksford
Significant misrepresentation of both 1-bit SDM and multi-bit LPCM coding paradigms persist within
both professional and commercial arenas that impacts directly upon the perception of DVD-A and SACD
formats. A balanced appraisal of these schemes is presented in order to expose the core differences in the
technology both in the theoretical and instrumentation domains. Some observations are made about the fallacy
of performance comparisons and the consequence of misinformation that subsequently is derived.
(AES paper 5397)
"DVD-Audio versus SACD: Perceptual Discrimination of Digital Audio Coding Formats" - Dominik Blech and Min-Chi Yang
Listening Comparison Test between DSD and High Resolution PCM (24-bit / 176.4 kHz)
To study perceptual discrimination between two digital audio coding formats, “Direct Stream Digital” and high-
resolution (24-bit, 176.4 kHz) PCM, subjective listening comparison tests were conducted with specially recorded
sound stimuli in stereo and surround.
To guarantee their reliability, validity and objectivity, the double-blind ABX tests followed three main principles:
The signal chain should be based on identical audio components as far as possible; these components should be able
to convey very high audio frequencies; and the test population should consist of various groups of subjects with
different listening expectations and perspectives.
The results showed that hardly any of the subjects could make a reproducible distinction between the two encoding
systems. Hence it may be concluded that no significant differences are audible.
(AES paper 6086)