When simulating a virtual reality, surfaces near the subject location can play a perceptual role. The authors studied the acoustic effect of nearby objects with both binaural response measurements and subjective listening tests. With a large, smooth, and flat surface, significant acoustical effects exist when the distance is less than about 50 cm. The largest effects can be attributed to comb filtering caused by the interaction between direct sound and reflected sound. At very short distances, some frequency-dependent resonances and shadowing effects that were evoked by the sound field between the subject and the surface could also be observed. Measurements showed some effects that could not be attributed to either simple comb filtering or resonance effects. In a listening test the subjects were asked to sort three binaurally-rendered samples in growing order of perceived distance. With relatively small distance triples, i.e., 1-11-21 cm, 3-13-23 cm, or 7-17-27 cm, the subjects performed better than guessing. However, even with shortest tested distances the proportion of correct answers was of the order of 50%. Two of 12 subjects consistently reported the distances in reverse order, which shows that the acoustic effect was significant, but it did not lead to the correct perception of distance of the surface. The results suggest that the acoustic effect of objects being close to an avatar’s ear may in some cases improve realism and sound quality in an acoustic virtual reality both in anechoic and in reverberant conditions.
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