Abstract: Research on how different compression schemes affect hearing aid users has examined the effects of compression speed. The pros and cons of different compression strategies have been used as arguments for systems that combine slow and fast elements. This argument may be taken one step further in suggesting that compression should be customized to the individual hearing aid user and their situation. We discuss how this may be done in different clinic and daily-life scenarios, and how personalization and user-driven customization may help the hearing care professional offer services that are distinct from the one-size-fits-all of over-the-counter hearing aids.
Summary: Compression is how hearing aids address the reduced dynamic range of most hearing aid wearers. The basic idea is simple: to fit the whole dynamic range of environmental sound into the dynamic range of a hearing aid wearer with a given hearing loss, soft sounds are amplified relatively more and loud sounds relatively less. In practice, however, the implementation of compression varies depending on how several different handles are used. This session starts out by explaining the basics of different compression schemes, including how the compression ratios and knee points are set and how compression speed affects the amplification.
On this basis we discuss the research on how different compression schemes affect hearing aid users, focusing on the effects of compression speed, i.e. how quickly gain is decreased in response to increases in input (attack time) and how quickly gain is increased in response to decreases in input (release time). Particularly the effects of release time have been researched and debated.
The primary advantage of fast compression is that it quickly adapts to the input level and thus more quickly represents changes in the listening environment. This for instance makes soft sounds following loud sounds more audible. It also allows softer speech sounds, typically unvoiced consonants, to be amplified relatively more than louder speech sounds, typically vowels. However, these advantages come at a cost: fast changes in gain alter the temporal envelope of the signal which is problematic. On the most general level, it is detrimental to sound quality, but it also negatively affects speech intelligibility for hearing aid users with poorer working memory or heavier hearing losses.
Conversely, slow compression preserves the temporal envelope of the signal, allowing better sound quality and higher naturalness, while also being beneficial for the speech understanding of those with poor working memory capacity and heavier hearing loss. The risk is reduced audibility for soft sounds following loud sounds.
These different pros and cons have been used as arguments for systems that combine slow and fast elements. This argument is still valid but may be taken one step further in suggesting that compression should be personalized to the individual hearing aid user. We discuss how this may be done in different clinic and daily-life scenarios, and how personalization may help the hearing care professional offer services that are distinct from the one-size-fits-all of over-the-counter hearing aids.
Learning Objectives:
Describe the basic handles of different compression schemes.
Analyze the pros and cons of fast and slow compression.
Evaluate the idea of personalized and customized compression settings.
