Threshold-based fitting methods for non-linear (WDRC) hearing instruments - comparison of acoustic characteristics

Six threshold-based prescriptive methods for non-linear hearing instruments were compared for a standard audiogram and three simulated listening situations. Six hearing aids were programmed according to the manufacturers' recommended initial fittings for the specified audiogram. Coupler gain measurements were then made with speech-like signals, and loudness and speech intelligibility index (SII) were calculated. Large differences between estimated insertion gain-frequency responses were seen. These differences resulted in large differences in calculated loudness, whereas the SII calculations showed only small differences between the fitting methods. For two of the methods, DSL[i/o] and FIG6, a comparison between the original prescriptions and the hearing aid manufacturers' implementations of the prescriptions was made. The results showed large differences between prescribed and implemented gain.