Doctor of Philosophy
Health and Rehabilitation Sciences
Macpherson, Ewan A.
Scollie, Susan D.
To improve speech intelligibility for individuals with hearing loss, hearing aids amplify speech using gains derived from evidence-based prescriptive methods, in addition to other advanced signal processing mechanisms. While the evidence supports the use of hearing aid signal processing for speech intelligibility, these signal processing adjustments can also be detrimental to hearing aid sound quality, with poor hearing aid sound quality cited as a barrier to device adoption. Poor sound quality is also of concern for music-listening, in which intelligibility is likely not a consideration. A series of electroacoustic and behavioural studies were conducted to study sound quality issues in hearing aids, with a focus on music. An objective sound quality metric was validated for real hearing aid fittings, enabling researchers to predict sound quality impacts of signal processing adjustments. Qualitative interviews with hearing aid user musicians revealed that users’ primary concern was understanding the conductor’s speech during rehearsals, with hearing aid music sound quality issues a secondary concern. However, reported sound quality issues were consistent with music-listening sound quality complaints in the literature. Therefore, follow-up experiments focused on sound quality issues. An examination of different manufacturers’ hearing aids revealed significant music sound quality preferences for some devices over others. Electroacoustic measurements on these devices revealed that bass content varied more between devices than levels in other spectral ranges or nonlinearity, and increased bass levels were most associated with improved sound quality ratings. In a sound quality optimization study, listeners increased the bass and reduced the treble relative to typically-prescribed gains, for both speech and music. However, adjustments were smaller in magnitude for speech compared to music because they were also associated with a decline in speech intelligibility. These findings encourage the increase of bass and reduction of treble to improve hearing aid music sound quality, but only to the degree that speech intelligibility is not compromised. Future research is needed on the prediction of hearing aid music quality, the provision of low-frequency gain in open-fit hearing aids, genre-specific adjustments, hearing aid compression and music, and direct-to-consumer technology.
Vaisberg, Jonathan Matthew, "Understanding hearing aid sound quality for music-listening" (2019). Electronic Thesis and Dissertation Repository. 6145.
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