3-D Audio Using Loudspeakers

3-D audio systems, which can surround a listener with sounds at arbitrary locations, are an important part of immersive interfaces. A new approach is presented for implementing 3-D audio using a pair of conventional loudspeakers. The new idea is to use the tracked position of the listener's head to optimize the acoustical presentation, and thus produce a much more realistic illusion over a larger listening area than existing loudspeaker 3-D audio systems. By using a remote head tracker, for instance based on computer vision, an immersive audio environment can be created without donning headphones or other equipment. The general approach to a 3-D audio system is to reconstruct the acoustic pressures at the listener's ears that would result from the natural listening situation to be simulated. To accomplish this using loudspeakers requires that first, the ear signals corresponding to the target scene are synthesized by appropriately encoding directional cues, a process known as "binaural synthesis," and second, these signals are delivered to the listener by inverting the transmission paths that exist from the speakers to the listener, a process known as "crosstalk cancellation." Existing crosstalk cancellation systems only function at a fixed listening location; when the listener moves away from the equalization zone, the 3-D illusion is lost. Steering the equalization zone to the tracked listener preserves the 3-D illusion over a large listening volume, thus simulating a reconstructed soundfield, and also provides dynamic localization cues by maintaining stationary external sound sources during head motion. This dissertation will discuss the theory, implementation, and testing of a head-tracked loudspeaker 3-D audio system. Crosstalk cancellers that can be steered to the location of a tracked listener will be described. The objective performance of these systems has been evaluated using simulations and acoustical measurements made at the ears of human subjects. Many sound localization experiments were also conducted; the results show that head-tracking both significantly improves localization when the listener is displaced from the ideal listening location, and also enables dynamic localization cues. Thesis Supervisor: Barry L. Vercoe Professor of Media Arts and Sciences This work was performed at the MIT Media Laboratory. Support for this work was provided in part by Motorola. The views expressed within do not necessarily reflect the views of the supporting sponsors. Doctoral Dissertation Committee Thesis Advisor Barry L. Vercoe Professor of Media Arts and Sciences Massachusetts Institute of Technology Thesis Reader William M. Rabinowitz Principal Research Scientist MIT Research Laboratory for Electronics Thesig§Reader David Griesinger Lexicon, Inc. Waltham, MA Thesis Reader Jean-Marc Jot Charg6 de Recherche IRCAM Paris, France