BSc (Natal), MSc (South Africa), PhD (Witwatersrand) – Professor Emeritus

Lab: PHY 205  Ext: 33755  Email:

Research Topics : Audio and electro-acoustics; Digital signal processing for audio; Diffraction and radiation of sound by loudspeakers; Electro-acoustic measurement techniques, Dither in image processing.

Present Research Activities: Both theoretical and experimental investigations are being made into the low-frequency radiation and diffraction of sound by loudspeakers. These are based on the use of the Helmholtz boundary integral formulation, and approximations thereto such as the Rubinowicz diffraction integral. It is hoped that this will lead to improved low-frequency measurement procedures in reverberant rooms.

The use of analogue as well as digital dithering techniques in digital audio, and digital signal processing in general, is being investigated both theoretically and experimentally. Dither can eliminate errors due to data quantization. Spectrally shaped dither signals and the design of dithered noise-shaping quantizers are specific current interests.

The application of digital signal processing techniques to audio promises to revolutionize the field in the next decade. We are pursuing investigations in such areas as room deconvolution, adaptive equalization, and surround- sound reproduction.

Some significant past papers

S.P. Lipshitz and J. Vanderkooy. 1983. A family of linear-phase crossover networks of high slope derived by time delay. J. Audio Eng. Soc. 31, 2-20.

J. Vanderkooy and S.P. Lipshitz. 1987. Dither in digital audio. J. Audio Eng. Soc. 35, 966-975.

J. Vanderkooy and S.P. Lipshitz. 1989. Digital dither: Signal processing with resolution far below the least significant bit. Proc. AES 7th International Conference “Audio in Digital Times”, Toronto, Canada, May 14-17, 1989.

J. Vanderkooy and S.P. Lipshitz. 1990. Uses and abuses of the energy-time curve. J. Audio Eng. Soc. 38, 819-836.

S.P. Lipshitz, R.A. Wannamaker, J. Vanderkooy and J.N. Wright. 1991. Non-subtractive dither. Proc. 1991 IEEE ASSP Workshop on Applications of Signal Processing to Audio and Acoustics, New Paltz, NY, October 20-23, 1991.

S.P. Lipshitz, J. Vanderkooy and R.A. Wannamaker. 1991. Minimally audible noise shaping. J. Audio Eng. Soc. 39, 836-852.

S.P. Lipshitz, R.A. Wannamaker and J. Vanderkooy. 1992. Quantization and dither: A theoretical survey. J. Audio Eng. Soc. 40, 355-375.

John Vanderkooy