Abstract:

A simple and widely used method for controlling the azimuthal direction of an apparent ``phantom'' sound source between two frontal loudspeakers is to vary the level difference between the (otherwise identical) signals delivered to the speakers. Explanations of phantom source localization [e.g., D. M. Leakey, J. Acoust. Soc. Am. 31, 977--986 (1959); B. B. Bauer, J. Acoust. Soc. Am. 33, 1536--1539 (1961)] have been based on the fact that, at low frequencies, the interaural phase delay in the dual-source stimulus matches that of an actual single source from some direction within the angular bounds of the loudspeakers. However, this theory fails to account for very similar localization results with stimuli that contain only high-frequency energy. It is also inconsistent with the perceptual robustness of the phantom image, which is unitary even with wideband stimuli. Leakey (1959) proposed that an interaural group delay underlies the high-frequency phantom. The present analysis of stimulus cues suggests that the interaural level difference may be an equally potent cue at high frequencies. Taken as a whole, this analysis points up the remarkable finding that this simple phantom-image technique results in the important interaural differences being well-matched to those of a single actual source across the audio spectrum. [Work supported by NIH.]