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In this study, a method for simulating the transfer function of a head-and-torso model over the entire audible frequency range is introduced. The simulation method uses the ultra-weak variational formulation (UWVF) which is a finite element type method tailored for wave problems. In particular, the UWVF uses plane wave basis functions which better approximate the oscillatory field than a polynomial basis used in the standard finite element methods (FEM). This leads to reduction in the computational complexity at the high frequencies which, accompanied with parallel computing, extends the feasible frequency range of the UWVF method. The accuracy of the new simulation tool is investigated using a simple spherical geometry after which the method used for preliminary HRTF simulations in the geometry of a widely used head-and-torso mannequin.

Being able to localize the position of a sound source is an important issue in robotics and many other application areas, since it enables those systems to interact with the environment. For example, USAR robotics can use sound to search for hidden victims that are shouting for help. The 2D binaural sound localization system in this paper is inspired by the human auditory system and is based on the lnteraural Time Difference (ITD) and the Head Related Transfer Function (HRTF). The ITD is used to localize a sound source in the horizontal plane relaying on the difference of arrival times of the sound signal between the two microphones and notches in frequency spectra (HRTF) are used to localize a sound source in the vertical plane. To easily and accurately extract notches we used a spiral shaped pinna that allows notches in the frequency spectra to change linearly as a sound source moves in the vertical plane, giving a relationship between notches and elevation angle. The two models used in this paper are tested to assess their accuracy, show their limitations and we concluded by noting how accuracy and repeatability can be improved.

A head-related transfer function (HRTF) is an acoustic transfer function between a sound source and the entrance of the ear canal. Since an HRTF is defined as an acoustic function of time and the sound source's location, the spatio-temporal frequency characteristics of HRTFs can be visualized and analyzed by multi-dimensional Fourier transform in time and space. In our experiments, we investigate the basic property of spatio-temporal frequency characteristics based on the coordinate system of measuring HRTFs on the horizontal plane and analyze the measured HRTFs. Moreover, the reverberation and pinnae effects of the spatio-temporal frequency characteristics are examined. As a result, the spatio-temporal spectrum components of HRTFs were mostly concentrated in specific frequency bands, and the spectrum components of other factors appeared clearly.

We investigated the influence on localization of simplifying HRTFs on the contralateral side. For the study described in this report, the spectral form of HRTFs are flattened in a region higher than a certain frequency. The results of a localization test suggest that the contralateral-side HRTFs at frequencies of 4 kHz or lower influenced front–back perception.