The Effects of Extended Input Dynamic Range on Laboratory and Field-Trial Evaluations in Adult Hearing Aid Users

Abstract

Digital hearing aids using a 16-bit analog-to-digital converter (ADC) provide a 96-dB input dynamic range. The level at which the ADC peak clips and distorts input signals ranges between 95 and 105 dB SPL. Recent research evaluated the effect of extending the input dynamic range in a commercially available hearing aid. Although the results were promising, several limitations were noted by the authors. Laboratory testing was conducted using recordings from hearing aids set for a flat 50-dB loss; however, field testing was conducted with hearing aids fitted for their hearing loss. In addition, participants rarely encountered input levels of sufficient intensity to adequately test the feature and were unable to directly compare aids with and without extended input dynamic range (EIDR) under identical conditions. The effects of EIDR under realistic and repeatable test conditions both within and outside the laboratory setting were evaluated. A repeated measures design was used. The experiment was single-blinded. Twenty adults (14 males and six females) between the ages of 30 and 71 years (average age 62 years) who were experienced hearing aid users participated. Each participant was fit with Oticon Opn hearing instruments binaurally using the National Acoustics Laboratory-Nonlinear 1 fitting strategy. Participants completed a two-week trial period using hearing aids with EIDR and a two-week trial period without EIDR. The initial EIDR condition trial period was counterbalanced. After each trial, laboratory evaluations were obtained at 85 dBC using the Connected Speech Test, the Hearing in Noise Test, and the acceptable noise level (ANL). Satisfaction ratings were conducted at 85 dBC using speech in quiet and in noise as well as music. Field-trial evaluations were obtained using the abbreviated profile of hearing aid benefit (APHAB). Satisfaction ratings were also conducted in the field at 85 dBC using speech and music. After the study, each participant indicated which trial period they preferred overall. Repeated measures analysis of variances were conducted to assess listener performance. Pairwise comparisons were then completed for significant main effects. In the laboratory, results did not reveal significant differences between EIDR conditions on any speech perception in noise test or any satisfaction rating measurement. In the field, results did not reveal significant differences between the EIDR conditions on the APHAB or on any of the satisfaction rating measurements. Nine participants (45%) preferred the EIDR condition. Fifteen participants (75%) indicated that speech clarity was the most important factor in determining the overall preference. Sixteen participants (80%) preferred the EIDR condition that resulted in the lower ANL. The use of EIDR in hearing aids within and outside the laboratory under realistic and repeatable test conditions did not positively or negatively impact performance or preference. Results disagreed with previous findings obtained in the laboratory that suggested EIDR improved performance; however, results agreed with previous findings obtained in the field. Future research may consider the effect of hearing aid experience, input level, and noise acceptance on potential benefit with EIDR.