Jacobsen, Simon
(2019)
Mitigation of comb filter effects by in-situ amplitude-phase measurements and gain table manipulation with a mobile hearing aid prototype.
["eprint_fieldopt_thesis_type_bachelor" not defined], Carl von Ossietzky University Oldenburg.
Abstract
Modern hearing aids are optimized for processing speech, but when dealing with more tonal non-speech sources like, e.g., music, the spectral perception can be altered due to comb filtering. Depending on the internal time delay and the level differences of direct and processed sound, certain frequencies may be amplified by up to 6 dB or alternatively cancel out completely, which may also be different for individual listeners. To avoid comb-filter effects with subject-specific fittings, the actual amplitude-phase-
relation at the eardrum of the listener has to be determined. An in-situ psychoacoustic measurement with a mobile hearing aid prototype is conducted in which the listener’s task is to find the amplitude and phase values to cancel out the direct sound at different frequencies. From the results, which show a significant conformity for the phase across all listeners and a slightly less pronounced conformity for the amplitude, a manipulation of the gain table is proposed to mitigate the effect of the comb filter. This approach could improve music perception for listeners or musicians with mildly impaired hearing. By aiming to preserve the natural sound, e.g., of musical instruments, it might also find application in a socalled “smart hearing protection” where direct sound will be a central issue.
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