DECS™: Testing the Idea

16th Oct, 2019

In the previous blog post, we discussed how an idea is developed and implemented into a hearing aid. I would like to talk about what happens once that idea becomes concrete and is available in a hearing instrument. At this point, we need to check that it functions in reality as well as it worked on paper. Engineers perform system tests to make sure that everything is implemented correctly and working as expected. However, just because something is technically working it doesn’t mean that it will have the same result on the end users. We need to test the subjective perception of the end users because this is the most important result. All of the work that we do in research and development is only successful if we can improve the end users’ listening experience.

Bernafon’s newest technological innovation, Dynamic Environment Control System (DECS), was created to help hearing aid users understand speech better in noise. There are four major components of DECS: Dynamic Amplification Control (DAC), Dynamic Noise Management (DNM), Dynamic Speech Processing (DSP), and Continuous Environment Detection. In the last blog post, Neil Hockley, described the DAC component in better detail. In this post, I will quickly describe the other components and then focus on how we tested the implementation of the entire DECS system.

Continuous Environment Detection analyzes the listening environment and collects the following information: input signal level, presence of speech, fast SNR estimator, and slow SNR estimator.

DNM combines the directionality and noise reduction into one unit allowing for communication between the algorithms. This communication helps the hearing aids apply the correct amount of directionality and noise reduction at each precise moment.

DSP uses the information provided by the Continuous Environment Detection, DNM, and DAC to apply the correct amount of amplification. The amplification is no longer based only on input level but on all of the information collected by the system.

Noise reduction, directional algorithms, and compression schemes have existed for many years. The existing algorithms for these features are generally reactive. They can change the noise reduction or the directionality mode once the system has determined in what type of environment that a user is. The problem is that the listening environment changes quickly. A typical classroom SNR can range from -6 to +6 dB (Crandell & Smaldino, 2000). A person can be in a restaurant having a conversation with people at the dinner table with the typical background noise of other talkers, dishes, etc. In an instant, this can change when a baby begins to cry loudly or when waiters begin to sing Happy Birthday to a customer. The environment has now become even more complex.

So how is DECS different from previous or other current systems? DECS has the ability to keep pace with these types of changes so that the listener’s conversation is not disrupted by the additional unexpected noise. Small changes in SNR will result in changes of the directionality, noise reduction, or amplification. These resulting changes may be subtle, but they should be. The listener can listen naturally without thinking about what type of environment they’re in, and whether the hearing aids are reacting appropriately. They should not notice or wait for the hearing aids to make changes in order to reduce background noise. They should notice that, yes, a baby has started to cry, but it should not impact their conversation. This is because DECS has already made adjustments to accommodate the deteriorating SNR from the baby’s cries. The point is not to shut the listener off from their environment. On the contrary, DECS was created with the goal of keeping the listener engaged in their environment but without negatively affecting their speech understanding or comfort.

So how did we check that this was actually working with end users? We ran a clinical trial. We ran a field test in which volunteer hearing aid users wore Bernafon hearing aids with DECS for two weeks and without DECS for two weeks and reported their experience. The design was double blinded meaning that the test clients did not know which settings they had and neither did the investigator. They were randomly mixed so that half of the group started with DECS and half started without. The clients completed a questionnaire as well as an interview with the investigator after each period. We collected all the comments made during the interview and grouped words that were most commonly used to describe their experience when using the DECS settings. The most common words used were intelligibility, comfort, balanced, environment, and natural. Additionally, here are some phrases quoted by individual test clients during the interview to describe their experience with DECS*:

  • “I’m more in the situation”
  • “I have a real stereo effect to locate and differentiate.”
  • “It’s almost like I used to hear before.”