カテゴリー連続判断法による自動車交通騒音の評価

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  • Rating of Road Traffic Noise using the Method of Continuous Judgment by Category
  • カテゴリー レンゾク ハンダンホウ ニヨル ジドウシャ コウツウ ソウオン ノ

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The present experiments were made to establish a relation between the overall judgment and the instantaneous judgment of the sound which continues over a long period. We have an impression of loudness of sound every moment, at the same time we may judge the overall loudness after some period passed. The overall loudness may be said to be a kind of summation of the loudness at each moment. To find the relation between them is very useful to expect the overall loudness. For this purpose, we have developed a new method, continuous judgment by category. Five subjects with normal hearing ability judged the impression of the sound of each moment using 7 categories from very noisy to very calm by touching one of the 7 micro-switches on the response box corresponding to each category. The stimuli used were nine kinds of road traffic noise with 1 minute duration recorded on a magnetic tape. They were reproduced by a tape recorder and presented to each subject through amplifier and loudspeaker. The responses of the subject were continuously recorded on the recorder. To obtain the overall judgment, two methods were used, semantic differential and the method of adjustment. In the experiment using semantic differential, the subjects were asked to judge the overall impression of the stimuli using 7 categories of three adjective scales, "noisy-calm", "clear-hazy" and "bass-treble", after listening to 1 minute stimulus. As for the method of adjustment, the result of our previous experiment was referred. The findings are as follows : (1) The coefficient of correlation between trials of each subject was so high that method of continuous judgment by category can be said to be reliable. Moreover, the subjective interval between categories was confirmed to be equal by Torgerson's law of categorical judgment. (2) High correlation was found between the sound level and the category scale of continuous judgment of the subjects at every one second (r=. 968). (3) The effect of the preceding stimulus was examined by calculating Leq averaging over 1 sec to 5 sec preceding to the judgment. 2 sec-averaged Leq showed the highest correlation with judgment. This fact suggests that the instantaneous judgment may be affected by the preceding stimulus and determined by averaging the sound level during 2 sec preceding to the judgment. (4) Though the overall judgment showed a high correlation with the average of instantaneous judgment of each changing stimulus, the latter showed a trend to be underestimated in the stimuli composed of 1 or 2 vehicles. This difference could be modified by excluding the judgment of the background noise from averaging. This fact suggests that the overall loudness is mainly determined by the prominent part of signals, and supports our previous finding that the overall loudness of level-fluctuating sound shows a high correlation with L_&lt10&gt or Leq, which are affected by the upper level of the sound. (5) From the findings of these experiments it was found that the overall loudness can be estimated by the instantaneous judgment or the instantaneous sound level. Our new method, continuous judgment by category, can be applied to any stimulus with longer duration. We would like to try it in the future.

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