In this paper, in order to evaluate quantitatively the stochastic characteristics of the fluctuating signal, a generalized n-th order fluctuation rate index is first proposed. Then, the high order equivalence relationship between two time constants of the ideal and the exponential type mean square operations is derived based on the proposed n-th order fluctuation rate index. More concretely, this equivalence relationship is newly discussed especially concerning the third order fluctuation rate index which occupies the first fundamental position in case of hierarchically evaluating the non-Gaussian property, and the well-known equivalence relationship T≅2γ(T: time constant of an ideal type mean squaring operation, γ: time constant of an exponential type mean squaring operation) is again found in a special case with n=2 from the different viewpoint in the time domain under the above same fluctuation rate index. The effectiveness of the proposed theory has been confirmed well experimentally by the applications to the actual sound data.

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A method to measure the acoustic holography by using a sub-array and a reference sensor has been used widely to reduce the cost of sensors and AD converters in the case that the sounds can be assumed to be stationary. However, it is difficult to find the best position of the reference sensor, since this method does not work well if the reference sensor picks up useless noise and reflections from the walls, floors or ceilings. Therefore, we propose a new method to measure acoustic holography by using a beamforming technique without the reference sensor. In the proposed method, the position of the original source which radiates the large sound power, is estimated by beamforming technique. By calculating the correlation function between the outputs of the beamforming, the, time lag due to the movement of the sub-array is compensated, and the compensated outputs of the beamforming are treated as a reference signal. It is found by computer simulations and an experiment that the estimation error due to the effect of other sound sources and reflections will reduce at most by about 10 dB by the proposed method using a sub-array with 15 sensors.

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The timbre of compound tones consisting of three amplitude modulated waves is examined by psychoacoustical experiments using a similarity judgement. The obtained data are analyzed by a multi-dimensional scaling (MDS) method. The MDS solutions are interpreted by the regression equations as a function of the envelope correlation coefficients between the AM waves. In particular, the envelope correlations between adjacent AM waves are the determinant factor. When the modulation rate is slow enough, the fine structure of amplitude envelopes of each AM wave affects the timbre. However, the modulation rate is faster than the auditory temporal resolving power, the fine structure has no effect and the timbre is determined by only the envelope correlations. The auditory system has a function to detect the amplitude envelope correlation between the output signals of the different auditory filters. The present study shows how this function contributes to timbre perception.

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To develop a measurement method for acoustic nonlinearity parameter B/A using an acoustic microscope, the second harmonic component of a focused Gaussian beam observed with a concave receiver, with an aperture large enough to cover the whole beam, set within the post focal region has been investigated. The theory based on the successive approximation solution for the Khokhlov-Zabolotskaya-Kuznetsov equation is validated through the experiment employing a 1.9-MHz focused ultrasound and a concave receiver. Both the fundamental and second harmonic amplitudes attain the maxima at the position where the multiple reflection signal produced between the source and receiver is well detected by the concave receiver. The phase of the second harmonic component relative to the fundamental is the same as that of the axial pressure in particular at this position. These are true even in the case with the insertion of a different liquid layer. The generation of the second harmonic, which corresponds to the linear and nonlinear acoustic properties of the different liquid, is observed with the concave receiver. This suggests that the B/A measurement utilizing the axial pressure of the focused beam may be extended to the data obtained with the concave receiver.

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