Digital audio systems are unlike conventional analog systems in which signals can be any value between a minimum to maximum and occur continuously in time. Digital audio systems use finite precision in representing signals and coefficients and in performing arithmetic operations. Consequently, system performance is determined by the precision that is used throughout the system. This paper discusses the factors that influence the performance of Infinite Impulse Response filters in high performance audio applications using fixed point arithmetic.
Convention Paper 5613

14:30 h
X2 A Re-evaluation of Fundamental Transform Structures for Efficient Implementation on Semi-Parallel DSP Architectures – Prabindh Sundareson, Texas Instruments, Bangalore, India

High performance DSPs have been used extensively for the implementation of signal transforms in transform based audio coders. While the first generation of DSPs featured single stage MAC (Multiple Accumulate) blocks, the current generation of DSPs feature dual-MAC hardware blocks. Though fast algorithms are available for implementation of transforms, a re-look at the algorithms from this semi-parallel architecture point of view is beneficial as it leads to more efficient implementations. This paper looks specifically at the family of lapped transforms, and quantifies the implementation efficiency of traditional fast optimizations on architectures with this type of semi-parallel computing capability, and derives algorithmic methods of increasing this efficiency.
Convention Paper 5614

15:00 h
X3 Trellis Noise-Shaping Converters and 1-Bit Digital Audio – Hiroshi Kato, Accuphase Laboratory, Inc., Yokohama, Japan

Just recently, a new type of delta-sigma converter, Trellis Noise Shaping Converter, has been introduced. When it is used to generate a bit stream in 1-bit digital audio format, its trellis structure with Viterbi algorithm enables more efficient use of data bits, which yields better performance in stability, signal to noise ratio and tonal behavior. It solves most of the performance problem caused by harsh non-linearity inherent in 1-bit quantization.
This paper briefly examines its architecture and performance. An emphasis is put on its simple and more predictable quantization noise spectrum in comparison with that of conventional modulators.
Convention Paper 5615

15:30 h
X4 Enhanced Sigma Delta Structures for SACD Applications – Derk Reefman, Erwin Janssen, Philips Research, Eindhoven, Netherlands

New Sigma Delta Modulators (SDMs) topologies for use in Super Audio CD (SACD) applications are introduced, called Sigma Delta Pre-Correction (SDPC), which allow the generation of ultra-high quality DSD. Spurious peaks, which are known theoretically to exist in SDMs, are present at levels well below -165 dB, even if undithered. Already a slight amount of dither, will further reduce these signals to levels which are with standard numerical precision undetectable.
Convention Paper 5616

16:00 h
X5 Improved Compression of DSD for Super Audio CD – Derk Reefman¹, Erwin Janssen¹, Mark Sandler², Joshua Reiss² - ¹Philips Research, Eindhoven, Netherlands; ²Queen Mary University of London, London, UK

A method is presented for improving current coding efficiency in DSD signals. The goal of this work is to explore new compression techniques which are tailored to the DSD format and which are meant to complement the current lossless DST compression practice used for SACD. The new technique builds on principles illustrated in previous papers. The method makes use of the highly oversampled character of DSD. Example implementations and results have been obtained. Losses to stability and signal-to-noise ratio have been measured and their audio effects have been minimized and quantified. Lower bounds are established on the compression ratio of these methods. This is viewed as a first step for a potentially constant bit rate compression scheme.
Convention Paper 5617

16:30 h
X6 Time-Quantized Frequency Modulation with Time Dispersive Codes for the Generation of Sigma-Delta Modulation – Malcolm Hawksford, University of Essex, Colchester, UK

Time quantization and noise shaping applied to linear frequency modulation (LFM) can form an alternative although unconventional means of generating 1-bit uniformly sampled code that is similar in structure to a feedback sigma-delta modulator (SDM). Fundamental insight into the SDM process and base-line coding spectrum emerges, where specifically linearity of signal conversion is studied and compared to that of linear pulse code modulation (LPCM). Time dispersive limiters both within and outside the noise shaper are investigated and their consequence on linearity explored. A noise averaging simulation reveals intrinsic distortion and noise modulation to be low when appropriate dither is used.
Convention Paper 5618

17:00 h
X7 The Effect of Idle Tone Structure on Effective Dither in Delta-Sigma Modulation Systems – James Angus, University of Salford, Salford, UK

This paper clarifies some of the confusion, which has arisen over the efficacy of dither in PCM and Sigma-Delta Modulation (SDM) systems. It presents a means of analyzing "in-band" idle tone structure and describes a fair means of comparison between PCM and SDM. It presents results, which show that dither can be effective in S-D systems.
Convention Paper 5619

17:30 h
X8 Toward a Better Understanding of 1-Bit Sigma-Delta Modulators - Part 3 – Stanley Lipshitz, John Vanderkooy, University of Waterloo, Waterloo, Canada

This is Part 3 of our ongoing investigation into the behavior of 1-bit sigma-delta modulators. It addresses the following topics:
(a) Angus has claimed that an undithered 1-bit sigma-delta modulator is effectively self-dithered by its internal noise. We show that his conclusion is essentially a quasi-dc one, and that his pictures of self-dither, although suggestive, do not in fact signify the elimination of all correlated artefacts in the way achieved by a properly-dithered multi-bit modulator.
(b) The “average-gain-plus-additive-noise” model of the 1-bit quantizer can be misleading as regards its nonlinearities, even though it may be useful for predicting its stability. We briefly discuss this issue.
(c) Some undithered modulators clearly show the production of subharmonic tones. We study the conditions under which this occurs.
(d) We also have some observations about why the integrated spectrum of many undithered 1-bit modulators is precisely conjugate-even about fS/4.
(e) The idle tone in a 3-level (i.e., 1_-bit) sigma-delta modulator manifests itself in a different way from that in a 2-level modulator. We study the effect of dither in suppressing the idle tone in both these topologies.
Convention Paper 5620

18:00 h
X9 Noise Shaping for Measuring Digital Sinusoidal Signal with Low Total Harmonic Distortion – Edward Semyonov, Tomsk University of Control Systems and Radio-electronics, Tomsk , Russia

The method of noise shaping consisting in minimization of quantization noise in neighborhood of harmonics of digital test sinusoidal signal is considered. This method provides quantization noise power on harmonics frequencies considerably smaller, than methods of noise shaping with uniform power spectral density. For example for 16 bit, 44100 Hz sampling frequency, -60 dB level, 1378 Hz test signal this method provides total harmonic distortion (THD) 0.00067% (without noise shaping THD=1.1%, with dither in a frequency band (20000-22050) Hz and a standard deviation 0.46 quantum THD=0.043%).
This method can be applied to measurement of nonlinearity of various systems (especially it is actual for DACs, digital filters and so on).
Convention Paper 5621