Thesis Format
Monograph
Degree
Master of Science
Program
Health and Rehabilitation Sciences
Supervisor
Scollie, Susan
Abstract
Research has indicated that the broad audible bandwidth available in current hearing aids is associated with increased loudness for high-level sounds, compared to older, limited hearing aid bandwidths (Van Eeckhoutte et al., 2020a). This thesis used increased compression ratios to investigate further the trade-off between loudness perception, speech intelligibility and sound quality, with adaptive and dual-path compression.
26 participants with mild to severe hearing loss were fitted bilaterally with Phonak Audéo P90-13T hearing aids to Desired Sensation Level method version 5.0 targets with varying compression ratios. The within-subject design included loudness scaling, consonant recognition, and sound quality ratings. Linear mixed models were used to analyze the data.
The results suggest that increasing the compression ratio reduced loudness without negatively affecting consonant recognition or sound quality. Differences between hearing loss groups indicate that the magnitude of increase to successfully reduce loudness perception depends on the degree of hearing loss.
Summary for Lay Audience
Hearing aids amplify sound signals to make them audible for people with hearing loss. Programming hearing aid amplification to the individual hearing loss is based on prescriptive amplification targets, such as the Desired Sensation Level method version 5.0 (DSL v5.0, Scollie et al., 2005; Seewald et al., 2005). Recent research indicated that fitting hearing aids that deliver amplification of very high-pitched sounds is associated with increased loudness for high-level sounds, compared to older hearing aids that only had amplification of low- and medium-pitched sounds (Van Eeckhoutte et al., 2020a; Van Eeckhoutte et al., 2020b).
Compression, which works like an automated volume control, is used in hearing aids to avoid making loud sounds too loud while making soft sounds more audible (Moore, 2007). However, high compression ratios that strongly reduce amplification combined with fast signal processing can distort the amplified sound signal and make it difficult for people with hearing loss to understand speech (Souza, 2002).
This study investigated the trade-off between reduced loudness perception and speech intelligibility for compression ratios equivalent to, and higher than, those used in DSL v5.0. The compression ratios were computed using a prototype software system that varied the compression ratio over a series of steps. Additionally, compression ratios were evaluated with two different compression types that resulted in hearing aid processing times. The study included 26 participants with mild to severe hearing loss and eligible for a hearing aid fitting in both ears. Participants were fitted with hearing aids that were programmed according to DSL v5.0 targets and hearing aid fittings were verified with acoustic measurements on participants’ ears. The test battery included loudness perception of speech in quiet, consonant recognition of soft and loud speech in moderate noise, and a sound quality rating of loud speech in moderate noise.
The results suggest that increasing the compression ratio in DSL v5.0 fittings reduced loudness without negatively affecting consonant recognition or sound quality. Differences between hearing loss groups indicate that the compression ratio required to successfully reduce loudness perception depends on the degree of hearing loss.
Recommended Citation
Voss, Solveig C., "Influence of compression in DSL v5.0 fittings on loudness perception and speech recognition in hearing-impaired adults" (2024). Electronic Thesis and Dissertation Repository. 10216.
https://ir.lib.uwo.ca/etd/10216