Establishment of a sound field reproduction method with high flexibility

具有高灵活性的三维声场的记录和再现对于远程协作系统中的高性能协作是重要的。本研究的目的是建立一种声场再现方法，以补偿双耳信号的个性，这是由两个麦克风嵌入在一个假人头部的两个耳朵记录（声学人体模型）并通过耳机再现。本研究项目涉及两种声场：一个是2005财年计划的死场，另一个是2006财年计划的混响场。房间的混响被观察为在房间中测量的声学传递函数中的峰和谷。当将阿尔马（自回归移动平均）模型应用于传递函数时，可以通过控制z平面中的极点和零点的数量和位置来控制混响。在2005财政年度，在这项研究中提出的补偿函数是通过平滑的传递函数减少极点和零点的数量。在2006财政年度，混响室的补偿函数是通过添加波峰和波谷得到的，波峰和波谷是通过使用阿尔马模型得到的。这些补偿功能的效果通过心理声学实验进行了评估。实验结果表明，在极点和零点数目足够的情况下，所提出的补偿函数对音质和声源定位都是有效的。结果表明，在远程协作系统中控制声场信息，无论说话人的面部图像如何，都能带来较高的文字可懂度.利用DSP（Digital Signal Processor）Starter Kit构建了一个双通道耳机耳道传递函数（Headphone-to-Ear-canal Transfer Functions，HpTF）测量系统。

Recording and reproduction of a three-dimensional sound field with high flexibility is important for high-performance collaboration in a tele-collaboration system. The purpose of this research is to establish a sound field reproduction method that compensates for individuality of binaural signals, which are recorded with two microphones embedded in the two ears of a dummy head (acoustical mannequin) and reproduced via headphones.Two kinds of sound fields were addressed in the term of this research project : One was a dead field intended in FY 2005 and the other was a reverberant field intended in FY 2006. Reverberation of a room is observed as peaks and dips in an acoustic transfer function measured in the room. When the ARMA (Auto-Regressive Moving-Average) model is applied to the transfer function, reverberation can be controlled by controlling the numbers and locations of poles and zeros in the z-plane. In FY 2005, a compensation function proposed in this research was obtained by smoothing the transfer functions with reduced numbers of poles and zeros. In FY 2006, a compensation function for a reverberant room was obtained by adding peaks and dips which were derived by using the ARMA model. The effects of these compensation functions were evaluated by psychoacoustical experiments. Experimental results show that the proposed compensation functions are effective for sound quality as well as sound localization if the numbers of poles and zeros are adequate.Besides the above mentioned research, the following two research items were undertaken :1. It was shown that controlling sound field information in a tele-collaboration system brings high word intelligibility irrespective of talking face images.2. A two-channel measurement system of HpTFs (Headphone-to-ear-canal Transfer Functions) was constructed using a DSP (Digital Signal Processor) starter kit.