Abstract:
A new method for on-line virtual sound source synthesis has been developed that affords direct comparison of virtual and real sound sources. Using this method, four listeners performed a 2AFC discrimination of real free-field sources and the virtual representations of these sources. The sources consisted of wideband noise bursts presented at a number of spatial positions. Virtual source fidelity was manipulated (on a trial by trial basis) by applying windows of various lengths (20.48, 5.12, 1.28, 0.32 ms) to the impulse responses (20.48 ms in duration) of the filters used to synthesize the virtual sources. When fidelity was highest, listeners could not discriminate virtual from real sound sources. As window length was decreased, discriminability increased. For a 1.28-ms window, performance was above 75% correct on average. These results are consistent with physical measurements of the differences in the acoustic signal at the listener's ear drum between virtual and real source presentation. In a related experiment, the same four listeners where asked to report the apparent positions of the virtual sound sources synthesized in the previous experiment. Degradation in localization performance was observed as filter window length was decreased. [Work supported by NASA.]