[A study on the effect of slower speech rate produced by the speech rate converter]

This study was concerned with the effect of the speech rate converter, invented by cooperation of NHK Science and technical research laboratories with the ENT Department, Tokyo Medical College. The converter can make the speech rate up to 1.6 times slower with little change in voice quality and personal features, so that the spoken language can be easily understood especially by aged people and foreigners. The test sentences consisted of 40 frequently used conversational sentences and 40 synthesized sentences, and were read by a female announcer at a rate of approximately 500 moras/minute and recorded on a DAT tape. Twenty-one subjects, with the average age of 77.4 years, were instructed to listen to each of the 20 sentences at the original speech rate and at the converted rate, and to repeat the sentences. In order to reduce the learning effect, these 40 sentences were randomized in speech rate and the order of presentation. The average loudness of these sentences was the most comfortable level for each subject. The results of this test showed that the correct answer rate for the converted rate sentences was significantly higher than for the original speech rate. Another test was performed to study the difference in remembering the sentences between the original rate and the converted rate. This study revealed that a sentence at the converted rate was more easily understood and could be easily memorized. At present, this device can be triggered by the incoming sound. Therefore, it is impossible to use it in a very noisy situation. In addition, the output is a little later than input, so the input voice is completely excluded from the ear canal when the device is used as a hearing aid. However, it can be used for a broadcast by mean of a special channel and for voices reproduced on a tape recorder, and this would be helpful for aged people.