Distance perception of a virtual sound source synthesized near the listener position

Abstract

This paper reports on the challenges faced in attempts to synthesize virtual sound sources near the listener position due to the differences between sound fields of real and virtual sound sources, especially if virtual sources reproduced by a line array of loudspeakers are to be positioned within the arm's reach of the listener. Distance perception has been described by various acoustical parameters, such as loudness, power spectrum, and direct-to-reverberant energy ratio; however, ILD has been considered as a strong distance cue when the source to be positioned near the listener and at an azimuth angle well offset from the median plane. The ILD observed in a sound field reproduced by a loudspeaker array is inevitably different from that of a real sound source due to several reproduction artifacts. Using a rigid sphere as a model of human's head within 1 m, we demonstrate how the ILD is influenced by the reproduction artifacts of a line array. Observing the ILD resulting for various virtual source locations shows that the acoustical cues to perceive distance are not well-reproduced in general; however, there are regions of virtual source locations near the listener within which correct ILDs can be provided. Some local minima in magnitude in space induce large ILD values at particular spatial positions through truncation of the array which results in virtual sources being positioned at extremely close range to the listener.