Head-related transfer function (HRTF) interpolation plays an important role for implementation of 3D sound system because it can not only reduce the number of measurements for HRTFs, but also reduce the data of HRTFs for seamless binaural synthesis. This paper addresses the problem of accurately realizing the interpolation of HRTF for synthesis of virtual auditory space, and proposes a HRTF interpolation method based on principal component analysis. Firstly, the HRTF is decomposed into principal components and corresponding principal component weights, where principal components are direction-independent and principal component weights are direction-dependent; then the directional variation of the principal component weight is multivariate polynomial fitted with a bivariate function of two spatial angulus (azimuth and elevation). Moreover, a sphere-partitioning optimization scheme is employed to improve the approximation precision. Experiment results demonstrate that HRTFs in the entire sphere surface can be interpolated by the proposed method with small distortion, and the proposed method performs better than conventional methods. Therefore the proposed method gives a promising way for HRTF interpolation.

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An airborne ultrasonic transducer is generally required to generate high sound pressure in order to realize precise detection and long-range measurement. The purpose of this study is to analyze the vibration mechanism of a piezoceramic transducer and to indicate guidelines for the optimum structure in order to increase the pressure amplitude. We focus our attention on the peak appearance in the pressure response of the transducer. We then clarify, experimentally and numerically, the sound radiation mechanism from vibrational and acoustical points of view. In this report, we present newly observed vibration modes with two peaks and promising schemes for efficiently increasing the sound pressure amplitude.

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Keyaki wood is the most suitable material for the “Wadaiko, a traditional Japanese drum.” However, the amount of wood with excellent quality available for producing the wadaiko has decreased in recent years. Wadaiko shells made of artificial materials are an effective substitute for the traditional wooden wadaiko. In this study, prototypes of the wadaiko were made using a wood plastic and their sound characteristics were examined. The vibrational properties of the wood plastic were investigated and compared with those of keyaki and sen woods used for the traditional wooden wadaiko. The sound characteristics of the wood plastic wadaiko were more complex than those of the keyaki wadaiko. The Chladni experiment on the wood plastic wadaiko clarified that the respective modal patterns appeared at two or three resonant frequencies with increasing the degree of the modes. The sound components of the wood plastic shell did not affect the overall sound characteristics of the wadaiko. The internal friction of wood plastic was larger than those of keyaki and sen, whereas the specific Young’s modulus in the grain direction was smaller than those of keyaki and sen. The results of this study indicated that the mechanical properties of wadaiko shell materials strongly affected both the tension of the membrane and the boundary condition between the membrane and shell. A large specific Young’s modulus as well as high strength comparable to that of keyaki is necessary for wood plastics to be used as a substitute material for the wadaiko shell.

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This paper considers wide-band DOA estimation using the spatial resampling method for coherent averaging. In this paper a rough estimate of the resampling error distribution is obtained. Careful examination of this distribution yields an improved resampling formula suitable for, but not limited to, arrays with finite sensors. It is shown that the proposed formula yields resampling error much less than that of conventional resampling. Moreover it is shown how the resampling error can be more reduced by proper choice of the focusing frequency. Based on the this resampling formula a perfect focusing scheme is then proposed and its performance is evaluated and compared to other wide-band methods through simulations. Simulations showed quite satisfactory and robust performance of the proposed scheme. It was shown that it succeeds in situations where all considered wide-band methods fail. In addition it is bias-free and can be implemented quite efficiently. Hence it is quite suitable for reliable real-time DOA estimation in reverberant environments.

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Distance measurement using an ultrasonic wave is suitable for environment recognition in autonomous mobile robots. Ultrasonic distance measurement with the pulse-echo method is based on the determination of the reflected echo’s time of flight (TOF). Pulse compression can improve distance resolution and the reflected echo’s signal-to-noise ratio (SNR). However, calculation of cross correlation requires high-cost digital signal processing. A sensor signal processing method of cross correlation using a delta-sigma modulated single-bit digital signal has been proposed. Cross correlation by single-bit signal processing reduces the calculation costs of cross correlation. Furthermore, cross correlation by single-bit signal processing improves the time resolution of the cross-correlation function. Therefore, the high-time-resolution cross-correlation function improves the distance resolution of the cross-correlation method. In this paper, ultrasonic distance measurement using cross correlation by single-bit signal processing is evaluated based on computer simulations and the experimental results.

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