Study of sound localization and its control

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This study aims at clarifying the factors that govern sound localization in our hearing system and at developing a method to control sound localization. To achieve these aims, first we developed new techniques to measure head related transfer functions(HRTF), very precisely. Moreover, we analysed the measured HRTF by using AR and ARMA analysis to consider how the locations of zeros and poles are related with the position of the sound source.Next, we simulated the derived HRTF's as precise as possible and convolved the simulated HRTF with a signal to be listened to. The simulated sound was given via headphones to test the accuracy of sound localization of the signal. The HRTF's were simplified by AR and ARMA techniques, and accuracy of sound localization when these simplified HRTF's were convolved with a signal. Moreover, mutual effects of sound images that were located at different positions were also examined. Finally, we considered a comprehensive method to localize a sound image at arbitrary position.Major findings of our study are as follows:1) Sound localization in a horizontal plane cannot be satisfactorily controlled by using only interaural time and level differences. 2) To control front/back of a sound image, it is necessary to take the effect of rotation of the head in to consideration as well as to simulate HRTF below about 5 kHz precisely.3) Elevation of a sound image can be correctly controlled only by simulating the HRTF above a few kHz rather approximately.4) Sound images located at different positions generally move to the opposite direction of the other image.5) As a whole, the most important factor to control localization of a sound is a head related transfer function(HRTF).