Hearing aid delay in open-fit devices – coloration-pitch discrimination in normal-hearing and hearing-impaired

Abstract

Objective

The delay in digital hearing aids is known to cause distortions due to the mixing of the delayed hearing aid sound with the undelayed direct sound. The most apparent delay-based distortion is a pitch sensation referred to as coloration-pitch. This study investigated coloration-pitch discrimination at the lower end of typical hearing aid delays and aimed at establishing thresholds where a large change in coloration-pitch is just perceptible.

Design

Simulations were verified against a reference hearing aid for numerous conditions of delay, insertion gain and incident direction. The simulations were used in a psycho-acoustics experiment in which coloration-pitch discrimination thresholds were measured as a function of hearing aid delay and gain. Participants discriminated between coloration-pitches produced by delay changes of 12%. Insertion gains compensating for mild to moderate hearing losses were used.

Study Sample

Nine normal-hearing and twelve hearing-impaired participants with mild to moderate hearing loss participated.

Results

The simulations accurately reflected the acoustics of the open-fit hearing aid. Discrimination thresholds were between 0.3 ms and 1 ms depending on insertion gain and hearing status.

Conclusions

High sensitivity for changes in coloration-pitch was found for delays >1 ms. For shorter delays participants were increasingly insensitive to changes in coloration-pitch.

Keywords:

• Hearing aid delay
• comb-filter effect
• coloration-pitch
• open fittings

Acknowledgements

The author thank colleagues at WS Audiology and three anonymous reviewers for very their thoughtful comments and discussions on earlier versions of this manuscript.

Disclosure statement

No potential conflict of interest was reported by the author.