Effects of frequency on free-field masking

As three-dimensional auditory displays become more prevalent, there will be an increasing need to understand the interactions that can be expected among spatially separated sounds. A two-alternative, forced-choice, adaptive staircase procedure was used to measure the detectability of a 165-ms click-train signal masked by a continuous Gaussian noise, as a function of the spatial separation between the signal and the masker in the free field. Horizontal separations within the horizontal plane and vertical separations within the median plane were examined for low-, mid-, and high-frequency stimuli. Masking was reduced by as much as 18 dB when the signal and masker were separated horizontally. Sizable reductions in masking (6-9 dB) were also observed for vertical separations. The largest reductions in masking were observed for the high-frequency stimuli. The data are compared with the results of headphone-based studies of binaural masking. Implications for the design of auditory displays are considered.