Recent developments in virtual acoustic imaging systems

This paper will present a brief review of progress in the development of loudspeaker-based systems for producing the illusion in a listener of the existence of a virtual source of sound at a pre-determined location relative to the listener. A fundamental consideration in the design of such systems is the conditioning of the matrix of transfer functions relating loudspeaker inputs to the signals reproduced at the listener’s ears. This plays a major part in dictating the bandwidth of effective operation of such systems and a brief description will be given of loudspeaker/listener geometries for ensuring successful operation over a wide band of frequencies. The efficient implementation of inverse filters that ensure the reproduction of the desired signals at the ears of the listener is an important issue and recent developments in filter design procedures will be outlined. The sensitivity of performance to listener position will also be discussed and suggestions given for the rate of adaptation required of the audio signal processing system if the illusion is to be preserved under conditions of a moving listener. Finally, a review of strategies will be presented for tracking the position of the listener by processing optical images of the space in which reproduction is sought.