PP317 - Optimizing Compression Settings for Speech and Music in a Direct Drive Hearing Aid

Abstract: Oftentimes application of compression to hearing aid fittings can be a confusing experience for clinicians due to existing and not to mention outdated recommendations. This study evaluated the impact of changing compression time constants on sound quality and speech clarity ratings in a compressor designed to maximize speech audibility by allowing maximum compression ratio to be 10:1. No sounds artifacts were noted for both slow and fast time constant conditions. Recommendations for optimal compression parameters for speech and music will be discussed.

Summary: Rationale:
In a normal hearing cochlea, compression is applied by outer hair cell activity to encode the large dynamic range of natural hearing. Sensorineural hearing loss results in loss of this non-linearity, resulting in reduced dynamic range and abnormal loudness growth. Accordingly, the application of compression to the processed output of a hearing aid is necessary and appropriate for the treatment of SNHL. However, clinicians are often faced with the dilemma of trying to optimize compression settings for various environmental conditions. Varied and oftentimes outdated recommendations exist for application of compression, for example, limiting maximum prescribed compression ratios to 3:1. A direct drive hearing device implementing the CAM2 fitting algorithm allows prescription of maximum compression ratios of up to 10:1 by using a slow-acting wide dynamic range compressor. In our previous presentation (Mandikal Vasuki et al., AAA 2022), we showed that higher compression ratios can be effectively applied without the deleterious effects on sound quality that have been reported with faster acting compressors in acoustic hearing aids. With careful optimization of time constants, hearing aid output can better reach prescription targets especially in a dynamic listening environment. In this study, we aim to evaluate the impact of various release times on sound quality ratings for speech in quiet, speech in noise, and music samples during laboratory and field listening when maximum compression ratio is 10:1.

Design:
Participants with bilateral mild sloping to severe sensorineural hearing loss were fitted with a direct drive hearing device and were enrolled in an IRB-approved within-subjects study. Two programs were created – a “slow” release time of 1000 ms and maximum compression ratio of 10:1 and a “fast” program with a release time of 200 ms and maximum compression ratio of 10:1. Participants were fit with the two programs in separate device memories with the order of programs counterbalanced across participants. Participants compared the perceived sound quality of the two programs by completing a sound quality questionnaire while listening to speech and music samples. They then conducted field comparisons of the two programs for one week. At the one-week follow up appointment, sound quality and speech clarity ratings were obtained using a modified version of the Glasgow hearing aid benefit profile (GHABP) questionnaire to compare the field listening experiences with the two programs. Preference data was also collected to determine whether the patients preferred one program over the other.

Results:
Results from pilot experiment show “fast” program was rated higher while listening to speech in the presence of soft background noise while “slow” program was rated higher for music listening. Listeners also rated “fast” program higher for situations evaluated using GHABP. Majority of the listeners did not have a preference for one program over the other after one week of field wear. Importantly, no sound artifacts were reported while listening through both programs.

Conclusions:
These findings support that with carefully selected compression parameters, listeners can experience benefits of compression such as increased audibility, more long-term speech loudness, and increased comfort without deleterious effects on sound quality.