It has been shown that HRTFs (Head Related Transfer Functions) are important cues for judging the absolute auditory distance of a single sound image when the sound source is close to the listener. In order to investigate the role of HRTFs in auditory distance perception more generally, not only the absolute distance of a single sound image but also the relative distances among multiple sound images should be considered. From this point of view, two kinds of psychoacoustical experiments on absolute and relative distance perception were conducted with the same source signals for stimuli. Comparison of the results of the two experiments showed that while the absolutely judged distance of a sound image increases with the actual distance of sound source up to around 1.2 m, the results of the relative auditory distance perception showed that the perceived distance significantly increases up to 2〜3 m. This difference may be attributable to some perceptual information stored in a short-term memory provided by the comparison of auditory distances between multiple sound images, which could offer an additional cue in relative distance perception, and it may be effective to improve the resolution of the distance perception of sound images at longer distance than the limitation in absolute distance perception.
