Where do ideas come from in hearing aid development? As with most technological endeavors, there is no easy answer to this question. At Bernafon, our ideas for development often come from looking at what has been done in the past, what is being discussed in the audiological research literature, and sometimes even what we imagine. Sometimes we have to adapt our ideas to achieve what we want due to technological limitations, but many times we are successful. A good example is how to amplify speech in the presence of noise. This has been something that we have looked at for a number of years and I would like to explain this to you in the context of the Dynamic Amplification Control™ (DAC™) feature within DECS™ – our brand new technology in the hearing instrument family Zerena 9|7|5.
Zerena’s new DECS™ technology featuring the
Dynamic Amplification Control™ (DAC™)
Without going into a lot of detail, speech perception is degraded for hearing-impaired people with a sensorineural hearing loss. There is a loss of cochlea resolution, which might be overcome by compressive amplification (Moore, 2014). With a loss of outer hair cells, there is a reduction of the active compressive system, while with a loss of inner hair cells there is a reduction in information transmission. Compressive amplification aims to restore audibility for softer signals while maintaining comfort for louder signals as an attempt to compensate for the loss of the outer hair cells. There are many instances where compression is not necessarily desirable, such as when speech is present with background noise. So how can we look at the environment and then disable the compression system when needed?
Our first attempt to change the compression system per environment was by using a feature in 2009 called Dynamic Contrast. When selected, the instrument would fade to a different gain setting when speech in noise was detected. Basically, the compression would be reduced from what the fitting rationale required. Within a year, we gave the option to select a different environment for the instrument to fade to with the Environment Optimizer (Bernafon AG, 2009). So it was possible to choose a single environment, instead of just speech in noise, such as quiet or noise (without speech present) where the gain could be adjusted when that specific environment was detected. These features were very well received but we started to think more about other possibilities that raised even further questions. Firstly, we wondered what would happen if there was more than one environment where the individual had some specific difficulties understanding speech. Secondly, we also thought about environments where one person’s definition of noise or speech in noise may not necessarily agree with another’s. Finally, we were concerned about the amplification of noise by the compression system after it had been reduced by the noise reduction and directional microphone systems. What we had previously developed was also static – there was only one set of gain adjustments that we could make. Could there be a dynamic way of adjusting the compression system continuously, depending upon the environment at any point in time, without using strict definitions of what that environment is?
Well, the answers to these questions resulted in our new feature called DAC. With DAC, the long-term and short-term SNR is continuously measured and analyzed. When the SNR is below a certain threshold, meaning there is more noise than speech, the compression is reduced in order to avoid over amplification during the natural pauses in speech. The resulting system is dynamic and seamless and is not limited by a hard classification of the environment – just the SNR. With DAC, we now have the technology to provide a solution to an issue that we first explored with changes in amplification in 2009. Our persistence has paid off and we are very proud to release this new feature in Zerena. We will write more about the new dynamic features that are found within Zerena in upcoming blog posts and publications. We hope that you will try DAC along with the other technology found in Zerena and share your experiences with us.
For more information about Zerena’s DECS technology including DAC, visit the DECS page on our website for professionals and sign up to our blog.
- Bernafon AG (2009). Topics in Amplification: Can we do more for speech-in-noise? Retrieved from http://www.bernafon.com
- Moore, B. C. J. (2014). Auditory Processing of Temporal Fine Structure: Effects of Age and Hearing Loss. World Scientific Publishing Company Ltd. Singapore.