Georg Essl - Research Projects

Banded Waveguides and Propagation Modeling: Efficient Physical Models of Solid Objects

with Perry R. Cook

Abstract: Propagation modeling by banded digital waveguides provides an efficient way of modeling the dynamics of solid objects. It is a generalization of digital waveguide filters to strongly dispersive systems. This model can be applied to objects of higher dimensions by exploiting inherent symmetries in the geometry. This way we developed efficient dynamical models for bar percussion instruments, indian tabla drums and wine-glasses. Complex, non-linear interactions are possible with these models and we demonstrate this by bowing bars and wine-glasses and by excerting complex bending interactions on the tabla model.

Fig 1: The most simple complete banded waveguide structure. BP are bandpass filters and DELAY are delay-lines.

Fig 2: Nodal symmetries of a circular membrane.

Papers:

Essl, G., Cook, P.R., "Sound Propagation Modeling in Solid Objects," submitted to IEEE Computer Graphics and Applications.
Essl, G., Cook, P.R., "Measurements and efficient simulations of bowed bars," Journal of the Acoustical Society of America, 108:1, 379-388, 2000. (pdf, ps)
Essl, G., Cook, P.R., "Banded Waveguides: Towards Physical Modeling of Bar Percussion Instruments," In Proc. Int. Computer Music Conf. (ICMC), Beijing, 22-28 October, 321-324, 1999. (ps)

Experiments on musical instruments 1: Bowed bar percussion instruments

with Perry R. Cook

Abstract: Bowing bar percussion instruments is an increasing part of the repertoire of modern composition and performance. Yet the system has not been studied systematically. We performed experimental measurements of bars of bar percussion instruments bowed by a double bass bow and by a bowing machine. They examine the relationships between performance parameters and perceptional parameters which are relevant for musical performance. Most measurement results are in good qualitative agreement with the known results of the bowed string. The spectrum of the bowed bar is observed to be harmonic, independent of the harmonicity or inharmonicity of the eigenfrequencies of the bar. But there are important distinctions. We found that the effect of bowing force and velocity on the
fundamental frequency and the spectral content does not show up in our measurements, suggesting that it is either very weak or independent. Independence is suggested by numerical simulation.

Fig1: Experimental Setup of manual bowing.

Fig 2: Multiple manual bows performed at increasing velocities. The resulting amplitude envelope increases with velocity.

Papers:

pdf

Experiments on musical instruments 2: Indian tabla drums

with Perry R. Cook and Ajay Kapur (undergraduate)

Abstract: We investigate complex stroke patterns as performed on indian tabla drums.

Fig 1: Ajay Kapur playing his tablas.
Fig 2: A pitch-bending GA stroke performed on the larger bayan-drum.

Papers: Work in progress.

Joint physical simulation of sound and graphics

with James F. O'Brien (Berkeley) and Perry R. Cook

Abstract: The goal of this work is to develop techniques for approximating sounds that are generated by the motions of solid objects. Our methods builds on
previous work in the field of physically based animation that use deformable models to simulate the behavior of the solid objects. As the motions of the objects are computed, their surfaces are analyzed to determine how the motion will induce acoustic pressure waves in the surrounding medium. The waves are propogated to the listener where the results are used to generate sounds corresponding to the behavior of the simulated objects. The simulations are compared to measurements of
actual objects and are found to be comparable.

Fig 1: Measured real vibraphone bar (left) and modeled virtual bar (right).

Fig 2: Comparison of measured, theoretical and predicted modes of bar.

Papers:

O'Brien, J.F., Cook, P.R., Essl, G., "Synthesizing Sound from Physically Based Motion," In Proc. SIGGRAPH 2001, Los Angeles, CA, August, 529-536, 2001. (pdf)

Links:

James O'Briens Project Page: Synthesizing Sounds from Physically Based Motion

Beat pattern extraction for musical genre classification

with George Tzanetakis and Perry R. Cook

Abstract: We extended musical genre classification schemes by extracting beat pattern data from music files. We utilize a wavelet decomposition scheme for this purpose.

Fig 1: Beat histogram of classical (left) versus rock music (right).

Papers:

Tzanetakis, G., Essl, G., Cook, P.R., "Audio Analysis using the Discrete Wavelet Transform," In Proc. WSES Int. Conf. Acoustics and Music: Theory and Applications (AMTA 2001) Skiathos, Greece, 2001. (pdf)
Tzanetakis, G., Essl, G., Cook, P.R., "Automatic Musical Genre Classification of Audio Signals," In Proc. Int. Symposium on Music Information Retrieval (ISMIR), Bloomington, Indiana, 2001. (pdf)

Multichannel Sound-Server Development and Spatial Audio through Soundfield Reconstruction

with Perry R. Cook, George Tzanetakis and Anoop Gupta (undergraduate)

Abstract: We develop single and multi-processor sound-servers to drive multiple speakers in conjuction with the large-scale display wall project and utilize the arrays of speakers to investigate soundfield reconstruction and other aspects of auditory display.

Fig 1: Basic architecture of the single-processor multi-channel sound server.

Papers:

Li, K., et al, "Early Experiences and Challenges in Building and Using A Scalable Display Wall System," IEEE Compter Graphics and Applications, 29-37, July/August, 2000. (pdf)
Cook, P.R., Essl, G., Tzanetakis, G., Trueman D., "N >> 2: Multi-speaker Display Systems for Virtual Reality and Spatial Audio Projection," In Proc. Int. Conf. Auditory Display (ICAD), Glasgow, 1-4 November, 1998. (ps)

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