In this study, we propose a method for non-contact visualization of sound fields, generated by an ultrasonic transducer, with the use of laser diffraction.The fundamental operational principle is based on optical computerized tomography(CT).The reconstructed, two-dimensional images are the amplitude and the phase distributions of the sound fields.In order to acquire this information of the sound fields, we used a laser beam as an optical probe.The laser beam passed through a sound field perpendicular to the sound beam and was detected without any optical system by a photodiode on the opposite side.In our experiment, we used a circular transducer driven at a frequency of 1.412MHz for a sound source.The experimental results were approximately in agreement with the results we obtained by measuring with a hydrophone.
In this paper, sound absorption characteristics of brick/block absorbing walls are investigated by the numerical analysis.A calculation method combining the wave scattering theory with the finite element method is introduced in order to make analysis on the sound absorption characteristics of brick/block walls with arbitrary neck shapes.The method is applied to hypothetical two dimensional brick/block absorbing walls, and it is found that the open-pipe resonance in a neck part and the standing wave in a backing space affect the sound absorption of the wall significantly at high frequencies.In addition, the method of controlling the sound absorption effect by changing the shape of the neck is investigated.The effect of changing the shape of the neck is confirmed by a 1/10 scale model experiment.
When a conventional word database is used to synthesize words, it was thought that a lack of pitch variety in synthesis segments was the major reason why the sound quality degradation occurred in the synthesized words.In order to reduce the sound quality degradation caused by pitch modification, we developed a word synthesis method taking into consideration the pitch variety in the database.The synthesis method uses a VCV-balanced word database consisting of words uttered forcibly in type-0 and type-1 accent patterns.This database contains the VCV-segments that are the same with regard to phoneme sequence but have different pitch patterns.We also improved the pitch modification process by using the techniques that the spectral features of each pitch waveform are adjusted according to the pitch modification, and the micro prosody inherent in the VCV-segment is retained.A pitch pattern matching measurement and a subjective evaluation confirmed the effectiveness of the new synthesis method as follows.(1)The total average of the pitch pattern matching distance obtained when the proposed database is used is approximately two thirds of that obtained when the conventional database is used.(2)The sound quality of synthesized words using the proposed database has marks more than 75% of preference score against that using the conventional database.
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