Development of TTS meter and evaluation on the hearing-effect of environmental sounds by using it

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We have developed a system which predicts TTS (Temporary Threshold Shift) in real time operation at actual noise induced fields. This system consists of a combination of a sound level meter with one-third-octave band filters and a multi-purpose personal computer.At first, a calculation procedure was considered to enable real time operation. In this consideration, it was found that the predicted value of TTS can be presented as the convolutional summation of the critical band spectrum level for the test frequencies and the impulse response obtained from the existing prediction equations. For Takagi's Prediction Equation, a time delay in the growth of the predicted TTS was observed, when the applicable conditions were processed by the same procedure for steady noise. An appropriate procedure to remove the time delay for time-varying noise was also considered. By using this system, we evaluated the effects of some environmental sounds on hearing in terms of TTS.