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

Area of Science:

• Audiology and Hearing Science
• Acoustics and Signal Processing

Background:

• Non-linear hearing instruments require precise prescriptive fitting methods for optimal performance.
• Existing prescriptive methods for hearing aids vary, potentially leading to different outcomes.
• Understanding the impact of different fitting strategies on audibility and speech intelligibility is crucial.

Purpose of the Study:

• To compare the performance of six threshold-based prescriptive fitting methods for non-linear hearing instruments.
• To evaluate the differences in estimated gain, calculated loudness, and speech intelligibility index (SII) across methods.
• To assess the accuracy of hearing aid manufacturers' implementation of selected prescriptive methods.

Main Methods:

• Six hearing aids were programmed using manufacturers' recommendations for a standard audiogram and simulated listening conditions.
• Coupler gain measurements were performed using speech-like signals.
• Loudness perception and Speech Intelligibility Index (SII) were calculated for each fitting method.

Main Results:

• Significant discrepancies were observed in the estimated insertion gain-frequency responses between the fitting methods.
• Calculated loudness showed substantial variations across methods, while SII calculations exhibited minimal differences.
• Large discrepancies were found between the prescribed gain and the actual implemented gain by hearing aid manufacturers for two methods (DSL[i/o] and FIG6).

Conclusions:

• Prescriptive fitting methods for non-linear hearing aids can lead to considerable differences in loudness perception.
• Speech intelligibility appears less sensitive to variations among these fitting methods compared to loudness.
• Hearing aid manufacturers' implementation of prescriptive formulas may deviate significantly from the original prescriptions, impacting device performance.