Study of sound localization and its control

本研究旨在阐明在我们的听觉系统中控制声音定位的因素，并开发一种控制声音定位的方法。为了实现这些目标，首先我们开发了新的技术来非常精确地测量头部相关传递函数（HRTF）。此外，我们还利用AR和ARMA分析分析了测量到的HRTF，考虑了零点和极点的位置与声源位置的关系。接下来，我们尽可能精确地模拟导出的HRTF，并将模拟的HRTF与要收听的信号进行卷积。通过耳机模拟声音，测试信号声音定位的准确性。利用AR和ARMA技术对HRTF进行了简化，并对这些简化后的HRTF与信号进行卷积后的声音定位精度进行了验证。此外，还研究了位于不同位置的声音图像的相互影响。最后，我们考虑了一种在任意位置定位声音图像的综合方法。本研究的主要发现如下：1)仅利用声间时间和声级差不能很好地控制声位在水平面上的定位。2)为了控制声音图像的前/后，有必要考虑头部旋转的影响，并精确模拟约5 kHz以下的HRTF。3)声像的高程只能通过近似地模拟高于几千赫的HRTF来正确控制。4)位于不同位置的声音图像通常会向与另一个图像相反的方向移动。5)总体而言，控制声音定位的最重要因素是头部相关传递函数（HRTF）。

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).