Acoustic Feedback in Hearing Aids

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Hearing aids are commonly fit with ear canals partially or fully open – a condition that increases risk of acoustic feedback.  Feedback limits the audiometric fitting range of devices by limiting usable gain.  To guide clinical decision-making and device selection, we developed the Peak Height Insertion Gain (PHIG) method – a novel way of detecting feedback spikes in the short-term insertion gain derived from audio recordings.  Using a manikin, 145 audio recordings of a speech signal were obtained from seven hearing aids.  Each hearing aid was programmed for a moderate high-frequency hearing loss with systematic variations in frequency response, gain, and feedback suppression; this created audio recordings that varied the presence and strength of feedback.  Using subjective ratings from 13 expert judges, the presence of feedback was determined and then classified according to its temporal and tonal qualities.  These classifications were used to optimize parameters for two versions of the PHIG method based on global and local analyses.  When specificity was fixed at 0.95, sensitivity of the global analysis was 0.86 and increased to 0.95 when combined with the local analysis.  Without compromising performance, a clinically expedient version of the PHIG method can be obtained using only a single measurement.

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