Electroacoustic evaluation of assistive hearing devices

The tests described here are the first steps in consumer-based hearing aid measures. Maximum length sequence broadband frequency response measurements provide a fast method to determine the accuracy of a hearing aid "fit". The aided output sound pressure level (SPL) graph adds valuable information to determining the fit: it clearly shows how the hearing aid compensates for a hearing loss; and relates the output SPL to the user's threshold, loudness discomfort level (LDL), and the desired sensation level long-term average spectrum of speech target for 70 dB input SPL. At a basic level, the question of user comfort is addressed by the SPL graph and biased frequency response testing. Exceeding a user's LDL may result in discomfort. Signal biased testing can be used to determine if environmental sounds are likely to cause unusual hearing aid operation, which may lead to discomfort. The type of processing used in a hearing aid can also be determined via pure-tone biased testing. The final questions of speech quality/intelligibility in various environments and the effect of hearing aid processing on listeners' performance and perception of sound quality are being addressed by the authors' current and future work. Objective measures of speech quality based on coherence have been used to predict subjective speech quality for normal listeners. There have also been a number of other objective measures of speech quality that have given good results over a wide range of distortions. The next step will be to apply these measures to hearing aid testing. This will allow one to make objective measurements of distortion and determine its influence on user comfort and judgment of speech quality.<
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