Ramani Duraiswami

Perceptual Interfaces and Reality Laboratory
University of Maryland, College Park

Joint work with Nail A. Gumerov and Adam E. O'Donovan.

Spherical Sound Scene Analysis

The sound arriving at a point is directional, and a spherical setting is the natural one to model it, as well as to measure it. In this talk I will explore two representations of directional sound - in terms of spherical wave functions and in terms of plane wave expansions. Error bounds for accurate representation, and the conversion between various basis will be presented. I will then discuss the capture of sound using spherical microphone arrays, and the conversion of the captured sound to these basis functions. Manipulation of the captured sound for various applications, such as HRTF based rendering for music and telepresence applications will be presented. In addition, application of the spherical array form to spatially selective sound capture (beamforming) will be discussed. Finally, I will present the use of spherical sound capture to create audio images. The registration of these images with visual images, and their joint use for audio-visual scene analysis will then be demonstrated. The talk will conclude with a discussion of open theoretical questions, and possible future applications.

Philip A. Nelson

Institute of Sound and Vibration Research,
University of Southampton

Joint work with F. Fazi and T. Takeuchi.

Inverse Problems and Sound Reproduction

A brief tutorial introduction will be given to the field of inverse problems. It transpires that several aspects of multi-channel sound reproduction can be analysed by using the theoretical framework provided by an extensive mathematical literature on this topic. An attempt will be made to explain important concepts such as ill-conditioning, regularisation and their implications in practical terms for the design of sound recording and reproduction systems. Such ideas can be most readily described with reference to the design of systems of relatively low order, but extend naturally to systems with a multiplicity of channels, and ultimately, to systems consisting of continuous distributions of sources and sensors. The analytical tools available also fit naturally into the framework of “spherical acoustics”.

Rozenn Nicol

3D audio technologies
France Telecom - Orange Labs

Sound spatialization by Higher Order Ambisonics: encoding and decoding a sound scene in practice from a theoretical point of view

An overview of HOA technology is presented. First, HOA defines a format of spatial audio which has many attractive properties, such as scalability and flexibility. Besides, this format is independent of the encoding (i.e. microphone signals) and decoding (i.e. loudspeaker signals) formats. Second, HOA provides tools to record, or create, and render a spatial sound scene. These tools, which rely on a specific encoding and decoding of spatial information, will be analysed and discussed from a both theoretical and practical point of view. Third, the final issue is the assessment of the virtual sound scene that is (re)created by HOA. The toolkit of available methodologies and criteria is examined.

Franz Zotter

Insitute of Electronic Music and Acoustics
University of Music and Performing Arts, Graz

Joint work with Hannes Pomberger (IEM) and Markus Noisternig (IRCAM).

Ambisonic Decoding With and Without Mode-Matching: Case Study Using the Hemisphere

Decoding and mode-matching has continuously been an interesting subject of many discussions in the Ambisonics community, and it can be expected to be the matter of future discussions and research as well. Technically, decoding by mode-matching can be seen as the attempt of a perfect sound-field resynthesis within a central area of limited radius, the sweet-area. Practically, the experienced Ambisonics listener knows that the results are not too bad outside this sweet area. So in practice, mode-matching may serve as not-so-perfect, but highly smooth Ambosonics decoding principle. But it is not the only way to Ambisonics decoding.