Fidelity of three-dimensional-sound reproduction using a virtual auditory display

The fidelity of reproducing free-field sounds using a virtual auditory display was investigated in two experiments. In the first experiment, listeners directly compared stimuli from an actual loudspeaker in the free field with those from small headphones placed in front of the ears. Headphone stimuli were filtered using head-related transfer functions (HRTFs), recorded while listeners were wearing the headphones, in order to reproduce the pressure signatures of the free-field sounds at the eardrum. Discriminability was investigated for six sound-source positions using broadband noise as a stimulus. The results show that the acoustic percepts of real and virtual sounds were identical. In the second experiment, discrimination between virtual sounds generated with measured and interpolated HRTFs was investigated. Interpolation was performed using HRTFs measured for loudspeaker positions with different spatial resolutions. Broadband noise bursts with flat and scrambled spectra were used as stimuli. The results indicate that, for a spatial resolution of about 6 degrees, the interpolation does not introduce audible cues. For resolutions of 20 degrees or more, the interpolation introduces audible cues related to timbre and position. For intermediate resolutions (10 degrees - 15 degrees) the data suggest that only timbre cues were used.