Study of sound localization and its control

本研究的目的是阐明声音定位在我们的听觉系统的因素，并在开发一种方法来控制声音定位。为了实现这些目标，首先，我们开发了新的技术来测量头部相关的传递函数（HRTF），非常精确。此外，我们还利用AR和阿尔马分析来分析HRTF的零极点位置与声源位置之间的关系，并对HRTF进行了尽可能精确的仿真，最后将仿真得到的HRTF与待测信号进行卷积。通过耳机给出模拟声音以测试信号的声音定位的准确性。通过AR和阿尔马技术简化了HRTF，当这些简化的HRTF与信号卷积时，提高了声音定位的准确性。此外，还研究了位于不同位置的声像的相互影响。最后，我们考虑了一种综合的方法来定位在任意位置的声像，我们的主要研究结果如下：1）声音在水平面上的定位不能令人满意地控制，仅仅使用两耳间的时间和水平差。2)为了控制声音图像的前/后，必须考虑头部旋转的影响，并且精确地模拟低于约5 kHz的HRTF。3）只有通过相当近似地模拟高于几kHz的HRTF才能正确地控制声像的仰角。4）位于不同位置的声像通常向另一个图像的相反方向移动。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).