The effect of a high upper input limiting level on word recognition in noise, sound quality preferences, and subjective ratings of real-world performance

Background: One important factor that plays a role in front-end processing is the analog-to-digital converter within current hearing aids. The average input dynamic range of hearing aids is 96 dB SPL with an upper input limiting level (UILL) of 95-105 dB SPL. The UILL of standard hearing aids could distort loud signals, such as loud speech or music, which have root-mean-square values of 90 and 105 dB SPL with crest factors of 12 dB SPL to 14-20 dB SPL, respectively. This indicates that these loud sounds could create a distorted signal for patients when the input limiting level is reached. Purpose: To examine if significant differences in word recognition in noise, sound quality preferences, and subjective ratings of real-world performance exist between conventional and high UILL hearing aids. Research Design: Words in noise and sound quality preferences were assessed using recordings on a Knowles Electronic Manikin for Acoustic Research with conventional and high UILL hearing aids, different microphone modes, and listening conditions. Participants wore the hearing aids for 2 mo and completed questionnaires on subjective performance. Study Sample: Ten adults with bilateral slight to moderately severe sensorineural hearing loss were recruited. Results: A four-factor repeated-measures analysis of variance (ANOVA) revealed significant differences between the conventional and high UILL across microphone modes and listening conditions for words in noise [F_{(2, 18)} = 6.0; p < 0.05]. A three-factor repeated-measures ANOVA for sound quality preferences revealed a significant difference only for presentation level [F_{(1, 9)} = 81.0; p < 0.001]. A one-factor ANOVA did not reveal significant differences between the conventional and high UILL on subjective ratings of real-world performance. Conclusions: Word recognition and sound quality preferences revealed significant differences between the conventional and high UILL; however, there were no differences in subjective ratings of real-world performance. One participant preferred the conventional UILL, two the high UILL, and seven thought performance was equal, which may be due to the listening environments participants encountered, as evidenced by datalogging.