technology
download
papers
about
contact
The following papers in portable document format (PDF) cover a range of audio signal processing fields, including low bitrate audio coding, sigma-delta modulation, digital interface jitter, and maximum-length sequence measurement.
C. Dunn, "Aspects of Scalable Audio Coding" [aes122.pdf, 191 kb], presented at the 122nd Convention of the Audio Engineering Society, Vienna, 5-8 May 2007, preprint 7081.
ABSTRACT - Banded weight data is transmitted as side information within coded audio bitstreams in order to achieve psychoacoustically-appropriate shaping of quantisation noise. Methods of reducing the information overhead corresponding to weight data are discussed in the context of scalable bitplane coding. Two approaches to coding band weights are compared in terms of coding efficiency and error resilience. In the first, weights are coded as a block of data at the beginning of each frame, using a predictor and Golomb coding of weight prediction residuals to achieve high coding efficiency. This approach is compared to coding weights for bands as they become significant, with weight data distributed across each coded bitstream frame.
C. Dunn, "Scalable Bitplane Runlength Coding" [aes120.pdf, 309 kb], presented at the 120th Convention of the Audio Engineering Society, Paris, 20-23 May 2006, J. Audio Eng. Soc. (Abstracts), vol. 54, p. 700 (2006 July/Aug.), preprint 6749.
ABSTRACT - Low-complexity audio compression offering fine-grain bitrate scalability can be realised with bitplane runlength coding. Adaptive Golomb codes are computationally simple runlength codes that allow bitplane runlength coding to achieve notable coding efficiency. For multi-block audio frames, coefficient interleaving prior to bitplane runlength coding results in a substantial increase in coding efficiency. It is shown that bitplane runlength coding is more compact than the best known SPIHT arrangement for audio coding, and achieves coding efficiency that is competitive with fixed-rate quantisation.
C. Dunn, "Efficient Audio Coding with Fine-Grain Scalability" [aes111.pdf, 146 kb], presented at the 111th Convention of the Audio Engineering Society, New York, J. Audio Eng. Soc. (Abstracts), vol. 49, p. 1235 (2001 Dec.), preprint 5492.
ABSTRACT - A comparison of audio coder quantisation schemes that offer fine-grain bitrate scalability is made with reference to fixed-rate quantisation. Coding efficiency is assessed in terms of the number of bits allocated to significant transform coefficients, and the average number of significant coefficients coded. A new method of arranging the transform hierarchy for SPIHT zero tree algorithms is shown to result in significantly improved performance relative to previously reported SPIHT implementations. Results for a new quantisation algorithm are presented which suggest low-complexity fine-grain scalable coding is possible with no coding efficiency penalty relative to fixed-rate coding.
C. Dunn and M. Sandler, "Psychoacoustically Optimal Sigma Delta Modulation" [jaes497.pdf, 762 kb], J. Audio Eng. Soc., vol. 45, pp. 212-223 (1997 Apr.).
ABSTRACT - A psychoacoustically-optimal sigma-delta modulator (SDM) possesses a noise floor with a power spectral density that is invariant with input signal characteristics, and which is also minimally-audible. While SDM idle tones and noise modulation can be efficiently eliminated using dither, the noise floor can be made minimally audible by forcing the noise-shaping characteristic to follow the threshold of hearing. Such an action is possible by appropriate control of noise-shaping zero locations, and has the benefit of increasing the perceived resolution of a given modulator design. Alternatively, for a given perceived resolution, psychoacoustically-optimal zero locations allow a reduction in oversampling factor and/or modulator order. In this paper optimal zero locations and associated enhancements in perceived resolution are determined for SDM orders ranging between 1 and 8.
C. Dunn and M. Sandler, "A Comparison of Dithered and Chaotic Sigma-Delta Modulators" [jaes496.pdf, 1704 kb], J. Audio Eng. Soc., vol. 44, pp. 227-244 (1996 Apr.).
ABSTRACT - Recent work has shown that higher-order single-bit sigma-delta modulators suffer from low-level artifacts such as idle tones and noise modulation. Techniques that have been proposed to reduce or eliminate these errors include the application of dither inside the one-bit quantiser loop, and selecting a loop filter which makes the modulator chaotic. This paper compares the efficacy of these two approaches by simulating high-resolution sigma-delta modulators suitable for audio-conversion applications.
C. Dunn and M. Sandler, "Efficient Linearisation of Sigma- Delta Modulators using Single-Bit Dither" [elet695.pdf, 306 kb], Elec. Letters, vol. 31, pp. 941-942 (1995 June).
ABSTRACT - Idle tones and noise modulation in higher-order sigma-delta modulators (SDMs) can be eliminated using single-bit dither signals, with no additional reduction in dynamic range compared to multilevel dither signals. Unlike multilevel dither, single-bit dither is easily implemented in sigma-delta analogue-to-digital converters (ADCs).
C. Dunn and M. Sandler, "Linearising Sigma-Delta Modulators using Dither and Chaos" [iscas95.pdf, 384 kb], Proc. 1995 IEEE Int. Symp. on Circuits and Systems, pp. 625-628 (1995 May).
ABSTRACT - Recent work has shown that high-order single-bit sigma-delta modulators suffer from low-level artifacts such as idle tones and noise modulation. Techniques that have been proposed to reduce or eliminate these errors include the application of dither inside the one-bit quantiser loop, and selecting a loop filter which makes the modulator chaotic. This paper compares the efficacy of these two approaches by simulating high-resolution sigma-delta modulators suitable for audio-conversion applications. Dynamic-range penalties for successful linearisation are determined for two types of dither signal and two classes of chaos.
C. Dunn and M. O. Hawksford, "Distortion Immunity of MLS-Derived Impulse Response Measurements" [jaes593.pdf, 2105 kb], J. Audio Eng. Soc., vol. 41, pp. 314 - 335 (1993 May).
ABSTRACT - Maximum length sequence (MLS) measurement of system impulse responses offers a potential enhancement in error immunity over periodic impulse testing, although care must be exercised in setting the MLS excitation amplitude in order to realise this potential. The effects of nonlinearity in MLS measurement are studied, in particular the way in which impulse response errors due to nonlinearity are distributed across the measurement period. The consequences of such errors in cumulative spectral display plots are also investigated. Finally inverse-repeat sequences (IRS) are shown to have complete immunity to even-order nonlinearity while maintaining many of the advantages of MLS.
C. Dunn and M. O. Hawksford, "Is the AESEBU/SPDIF Interface Flawed?" [aes93.pdf, 2452 kb], presented at the 93rd Convention of the Audio Engineering Society, J. Audio Eng. Soc. (Abstracts), vol. 40, p. 1040 (1992 Dec.), preprint 3360.
ABSTRACT - It is a requirement of high quality digital audio systems that all digital interfaces in the signal path exhibit signal transparency. The widely adopted AESEBU/SPDIF interface has received criticism from some quarters for a lack of signal transparency; this paper addresses possible problems with such interfaces and presents methods for improving the interface standard.