Measurement of distance perception using virtual audio

Relative auditory distance perception of a direct path signal by itself, with synthetic reflection(s), reverberation, presented over headphones, was measured using a 2AFC task. The stimulus, either a 500 millisecond pink noise burst or a two second phrase of male speech, was presented twice, first at a reference distance and second at an incremental distance from the reference. Reference distances include five, fourteen, and twenty-two feet, and the incremental distances included multiples of 0.25, 0.5, and 1 foot, respectively. Stimulus pairs at each of the three distances were presented from four directions: front, back, left, and right. For each stimulus pair, the task of three subjects was to indicate which of the two sounds appeared closer to himself/herself. From histograms for each condition, the just noticeable difference (JND) was calculated by determining the minimum interval at which the subjects could respond correctly seventy-five percent of the time. Virtual audio may help a pilot to perform a variety of functions in the military cockpit. The visual workload may be reduced by providing a spatial auditory beacon for navigation waypoints