Year

2006

Degree Name

Doctor of Philosophy

Department

School of Electrical, Computer and Telecommunications Engineering - Faculty of Informatics

Abstract

This thesis first presents a novel object-oriented scheme which provides for ex- tensive description of time-varying 3D audio scenes using XML. The scheme, named XML3DAUDIO, provides a new format for encoding and describing 3D audio scenes in an object oriented manner. Its creation was motivated by the fact that other 3D audio scene description formats are either too simplistic (VRML) and lacking in realism, or are too complex (MPEG-4 Advanced AudioBIFS) and, as a result, have not yet been fully implemented in available decoders and scene authoring tools. This thesis shows that the scene graph model, used by VRML and MPEG-4 AudioBIFS, leads to complex and ine±cient 3D audio scene descriptions. This complexity is a result of the aggregation, in the scene graph model, of the scene content data and the scene temporal data. The resulting 3D audio scene descriptions, are in turn, difficult to re-author and signifcantly increase the complexity of 3D audio scene renderers. In contrast, XML3DAUDIO follows a new scene orchestra and score approach which allows the separation of the scene content data from the scene temporal data; this simplifies 3D audio scene descriptions and allows simpler 3D audio scene renderer implementations. In addition, the separation of the temporal and content data permits easier modification and re-authoring of 3D audio scenes. It is shown that XML3DAUDIO can be used as a new format for 3D audio scene rendering or can alternatively be used as a meta-data scheme for annotating 3D audio content.

Rendering and perception of the apparent extent of sound sources in 3D audio displays is then considered. Although perceptually important, the extent of sound sources is one the least studied auditory percepts and is often neglected in 3D audio displays. This research aims to improve the realism of rendered 3D audio scenes by reproducing the multidimensional extent exhibited by some natural sound sources (eg a beach front, a swarm of insects, wind blowing in trees etc). Usually, such broad sound sources are treated as point sound sources in 3D audio displays, resulting in unrealistic rendered 3D audio scenes. A technique is introduced whereby, using several uncorrelated sound sources, the apparent extent of a sound source can be controlled in arbitrary ways. A new hypothesis is presented suggesting that, by placing uncorrelated sound sources in particular patterns, sound sources with apparent shapes can be obtained. This hypothesis and the perception of vertical and horizontal sound source extent are then evaluated in several psychoacoustic experiments. Results showed that, using this technique, subjects could perceive the horizontal extent of sound sources with high precision, differentiate horizontally from vertically extended sound sources and could identify the apparent shapes of sound sources above statistical chance. In the latter case, however, the results show identification less than 50 % of the time, and then only when noise signals were used. Some of these psychoacoustic experiments were carried out for the MPEG standardisation body with a view to adding sound source extent description capabilities to the MPEG-4 AudioBIFS standard; the resulting modifications have become part of the new capabilities in version 3 of AudioBIFS.

Lastly, this thesis presents the implementation of a novel real-time 3D audio rendering system known as CHESS (Configurable Hemispheric Environment for Spatialised Sound). Using a new signal processing architecture and a novel 16-speaker array, CHESS demonstrates the viability of rendering 3D audio scenes described with the XML3DAUDIO scheme. CHESS implements all 3D audio signal processing tasks required to render a 3D audio scene from its textual description; the definition of these techniques and the architecture of CHESS is extensible and can thus be used as a basis model for the implementation of future object oriented 3D audio rendering systems.

Thus, overall, this thesis presents ontributions in three interwoven domains of 3D audio: 3D audio scene description, spatial psychoacoustics and 3D audio scene rendering.

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