A numerical form for the radiation coupling between two co-axial disks separated by a medium exhibiting acoustic absorption shall be presented. This method has been used to show that diffraction and absorption can be treated as two separable processes. The radiation-coupling gain is applicable to the correction of the experimental data. The results are compared with published theoretical data.

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Utilization of blind signal separation method for the enhancement of speech recognition accuracy under multi-speaker is discussed. The separation method is based upon the ICA (Independent Component Analysis) and has very few assumptions on the mixing process of speech signals. The recognition experiments are performed under various conditions concerned with (1) acoustic environment, (2) interfering speakers and (3) recognition systems. The obtained results under those conditions are summarized as follows.(1) The separation method can improve recognition accuracy more than 20% when the SNR of interfering signal is 0 to6dB, in a soundproof room. In a reverberant room, however, the improvement of the performance is degraded to about 10%.(2) In general, the recognition accuracy deteriorated more as the number of interfering speakers increased and the more improvement by the separation is obtained.(3) There is no significant difference between DTW isolated word discrimination and HMM continuous speech recognition results except for the fact that saturation in improvement is observed in high SNR condition in HMM CSR.

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This paper describes a new trial to estimate the statistical input-output relationship of complicated sound insulation systems in an actual situation when the input-output data are roughly observed due to the level-quantization mechanism of measuring equipment, especially from a practical viewpoint. Then, the output probability distribution for another kind of input can be predicted by using the estimated regression relationship. Finally, the effectiveness of the proposed method is experimentally confirmed by applying it to the actually observed data.

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In this paper, we propose a practical system for private communications with chaos using digital signal processor (DSP). Recently, many analog circuits for private communications with chaos have been proposed. The core technique of this method is based on the strict parameter matching between the transmitter and the receiver system. However, it seems difficult, at least practically in analog circuits, to match the transmitter parameters with the receiver parameters for a long time. Therefore, we try to use the DSP for modulation and demodulation systems by assuming the digital transmission line such as computer networks. Today the DSP has calculation performance over 10 MIPS, therefore, almost all the calculation processes for modulation and demodulation can be performed in real time in audio frequency range. We investigate the round-off error problem peculiar to the fixed point DSP with finite bit length variables, and then propose a new algorithm that can overcome this problem to achieve perfect information recovery characteristics using the 16-bits fixed point DSP.

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