[Effect of frequency compression in hearing aids on speech intelligibility and subjective sound quality]

The acceptance of hearing aids by users with high frequency hearing loss still represents a problem. Processing algorithms that shift high frequency signal components into an audible frequency range are proposed as a solution. We looked into the issue of whether frequency compression becomes more beneficial with increasing high frequency hearing loss or/and for users with cochlear dead regions (DR).

A total of 20 hearing aid candidates were assessed audiometrically and classified into two test groups in terms of their hearing loss and the presence of DR. The subjects then evaluated four hearing aid settings that differed solely in the degree of frequency compression. Speech recognition threshold measurements and subjective sound quality ratings were carried out for all four settings.

Data showed that 15 of the 20 test subjects understood fricatives with a high frequency spectrum component better, since they were able to distinguish between the two logatomes "Afa" and "Asa". No correlation was found between the beneficial effect of frequency compression and the degree of high frequency hearing loss or the presence of DR. Subjective sound quality ratings indicated no clear preference, but excessive frequency compression was generally deemed counterproductive.

Frequency compression may be appropriate for hearing aid users with high frequency hearing loss and can improve speech recognition. The degree of frequency compression required to achieve maximal benefit varies from case to case and has to be optimized on an individual basis.