A comparative study of the sound characteristics of hearing aids through the International Speech Test Signal.

Abstract

　In 2012, the IEC published a document entitled, “Methods for characterizing signal processing in hearing aids with a speech-like signal” (IEC 60118-15), and the Japanese version (JIS C 5516) was subsequently issued in 2015. According to this document, we analyzed the long-term average speech spectrum (LTASS) and percentile of the sound pressure level (Percentile) of four hearing aids, and compared them under an on or off condition of various functions. We also evaluated the LTASS and Percentile, as well as the result of evaluation according to the “Guideline for the evaluation of hearing aid fitting” in 50 hearing aid users.

　The results showed that all of the four different hearing aids showed the same pattern of the frequency diagram, regardless of whether various functions were on or off. And also we found few discrepancies between the results of hearing aid fitting evaluation and the Percentile. However, the international speech test signal (ISTS) was found to be a more useful to measure the acoustic characteristics of hearing aids for the ‘normal wear' setting.