Study for practical use of a digital hearing aid device having functions of speech rate convertion and intonation emphasis

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The purpose of this study is to develop a digital hearing aid, which has functions of speech rate conversion and intonation emphasis, for the elderly impaired. Research results are as follows.1. The digital hearing aid having a function of the speech rate conversion was designed and this hearing aid was evaluated by the elderly hearing impaired. From the experimental results, the recognition rate of the Japanese words increased 3 times when the conversion rate was 1.5 times of the ordinary speech rate. We have developed a portable hearing aid having the speech rate conversion function in cooperation with Hitachi company.2. Discrimination ability of the intonation change was tested by the elderly hearing impaired. From the results, the ability was found to be much worse than the normal subjects. Furthermore, the intonation discrimination ability of the elderly hearing impaired was found to increase when the intonation of the words was emphasized. This means that the intonation emphasis was effective for the hearing impaired. Especially, the emphasis would be useful for Chinese spoken language which has fore tones.3. We have found that pitch fluctuation, which is small intonation change, has characteristics of 1/f fluctuation. It was anticipated that the addition of the fluctuation to the hearing aid function would be useful to improve the quality of speech. Furthermore, a wavelet conversion method was proved to be effective to control the pitch fluctuation and the conversion algorithm was successfully stored into a digital signal processor of the hearing aid. Through the study, it was clarified that the 1/f fluctuation and the wavelet conversion algorithm are very useful to improve the digital hearing aid for the elderly hearing impaired.