Center and Spatial Extent of Auditory Events as Caused by Multiple Sound Sources in Frequency-Dependent Directions

In everyday life, humans often perceive complex auditory events. Many natural sound sources are not point-like, but spatially extensive. Also, sound reproduction techniques sometimes produce virtual sources whose directional cues propose multiple directions at a time. Perceptual mechanisms for decoding the perceived direction and the spatial distribution of such auditory events are not well known. This paper investigates how sound objects whose localization cues indicate different azimuth direction as a function of frequency, 1) are localized, and 2) how horizontally wide they are perceived. A horizontally wide (45°) sound source was created by presenting spectrally consecutive, non-overlapping, bandlimited noise samples simultaneously from the different loudspeakers of a loudspeaker grid in an anechoic environment. The narrowband samples together formed a broadband stimulus. The order of the narrowband noise samples in the loudspeakers, as well as the total frequency range of the samples, was varied from case to case. In each test case, the subjects were asked to indicate the perceived center of gravity of the sound image, as well as the direction of all the loudspeakers that they perceived to radiate sound. Generally, the perceived center could not be predicted merely by a simple model using Raatgever's frequency weighting function for binaural salience [1]. Alternative frequency weights were calculated analytically from the listening test results. The results also indicated that the perceived width of the sound sources produced by the nine-loudspeaker setup was, in all cases, less than half of the actual width of the source. This implies that some frequency bands from different loudspeakers fused together spatially.