A Method to Remove Differences in Frequency Response Between Commercial Hearing Aids to Allow Direct Comparison of the Sound Quality of Hearing-Aid Features

Abstract

Goal: We want to remove differences in frequency response between different commercial hearing aids so that we can compare the sound quality of signal processing features from different hearing-aid in a future paired-comparison set-up. More specifically, we want to control for the confounding effects of the linear hearing aid response when evaluating nonlinear processing. This article presents a control procedure and evaluates its effectiveness. Method: We increased the similarity of hearing-aid recordings in three steps and used both an objective quality metric and listening tests to investigate if the recordings from different hearing aids were perceptually similar. Results: Neither was it sufficient to manually adjust the hearing-aid insertion gain, nor was it sufficient to add an additional bandwidth limitation to the recordings. Only after the application of an inverse filter the perceptual differences between recordings were removed adequately. Conclusion: It was possible to level the ground between different hearing devices, so to speak. This will allow future research to evaluate the sound quality of nonlinear signal processing features.

Perceptual Effects of Noise Reduction With Respect to Personal Preference, Speech Intelligibility, and Listening Effort

“…Houben et al (2011a) conducted several tests to verify whether their methods for hearing aid fitting, recording, and filtering indeed removed all the perceptual differences among recordings from different hearing aids with all the processing features deactivated. The only difference among hearing aids is then caused by the noise reduction because all hearing aids are perceptually equal when noise reduction is turned off.…”

“…Houben et al (2011a) developed and evaluated a method that allows for direct comparison of noise-reduction systems of different hearing aids, without the confounding effects of other hearing aid characteristics. If we were to find substantial differences among subjects even in this homogeneous group of listeners, these differences would be caused by individual differences because there would be no differences in hearing ability to confound the results.…”

“…The hearing aid numbers used in this study were randomly assigned to the test hearing aids and are different from the numbers used in Houben et al (2011a). This selection was a representative sample of the commercial hearing aids available at the time of the study.…”

“…We applied the same methods of hearing aid fitting and recording as described by Houben et al (2011a). In fact, we took the hearing aids, hearing aid settings, and equalization filters from their test set, so that we were sure that their verification of the method was also applicable to our recordings.…”

“…The recording and filtering technique developed by Houben et al (2011a) allowed us to compare all combinations of noise-reduction systems directly with each other in a paired-comparison design. The recording and filtering technique developed by Houben et al (2011a) allowed us to compare all combinations of noise-reduction systems directly with each other in a paired-comparison design.…”