GN Hear & Now

RESOUND EXPERT

BINAURAL DIRECTIONALITY III

Our natural auditory processing skills allow us to differentiate between important sounds such as speech over other environmental sounds e.g. noise, music etc.
We have the ability to filter our sound environment to either suppress or enhance the sounds of interest depending on our level of focus, which is an amazing feature of our brain.
Contrary to belief, this natural ability does not disappear when a hearing loss creeps up on us. The ability to focus on several sounds at the same time is just as prevalent in people with hearing loss as it is with normal hearing people. The key to achieving this lies in the strategy of the hearing aids’ automatic features and how these are configured for the hearing impaired wearer.

Three factors are important to provide this seamless, natural listening experience. 

  • Firstly, the hearing aids have to analyse the acoustic environment precisely. 
  • This information is then fed into the hearing aid decision making algorithm which is a critical component of the process. 
  • Finally the directional processing itself has to provide a signal to noise ratio improvement but without losing audibility or sound quality.

If the hearing aid cannot determine the sound environment correctly then the automatic features of hearing aids will be set up inappropriately and therefore provide the wearer with an “alternative” sound environment to the actual sound environment. For example, if a hearing aid wearer walks through a shopping mall conversing with their friend who is beside them, with music playing in the background, the friend is the signal of interest and the music is background noise. If the hearing aid determines the music to be the signal of interest then the hearing aid wearer will not achieve optimal audibility for the conversation with their friend.

When ReSound first introduced Binaural Directionality into our hearing aids, we offered a system that provided directional benefit while allowing the user to hear more of what is around them.
With Binaural Directionality IIITM in the ReSound LiNX 3DTM range, we have further improved on our already superior directionality, helping wearers to have even better 360⁰ awareness of sounds around them and allowing them to use their natural ability to focus on the sound of interest with little effort.

Figure 1. ReSound was 98% accurate in identifying speech-in-noise in varying noise backgrounds. No other system was as accurate, and noise backgrounds with music or highly modulated noises posed the greatest difficulty for these systems. Accurate identification of speech in noise and other environments is important in adjusting environmentally dependent parameters accurately.

A recent study showed that ReSound LiNX 3D is up to 50% better than other premium hearing aids* at identifying speech in various environments. Wearers can hear 80% more of the sounds around them and understand 40% more speech in noise**.

The graph above shows that ReSound is 98% accurate in identifying speech-in-noise environments. This was tested with speech in the presence of various types of background noise. We compared ReSoundLiNX 3D against 5 other manufacturers’ premium products. Devices were set up to be fully automatic, were exposed to a known sound and then we compared their data logging results to the actual sound environment.
The results are compelling, with ReSound LiNX 3D providing the most accurate identification of the listening situation, while the poorest performing competitor device only classified a speech-in-noise environment accurately 42% of the time.

Furthermore, we wanted to confirm the functionality of Binaural Directionality III. In the test set up shown below, three speakers playing noise are positioned around the user, one behind and two on either side of the hearing aid wearer. These are the white triangles in the diagram.

While noise was playing from these speakers, the other speakers indicated by the green and red triangles, each simultaneously presented a different sentence. The target speech (green triangle) was a sentence starting with the word Dagmar (a Danish female name). The subject had to listen for the sentence starting with Dagmar and repeat back that sentence.

In this environment, ReSound LiNX 3D identified three speech signals from three different directions, the front, the left and from behind. Binaural Directionaliity III therefore set up the left aid in an omnidirectional polar pattern, in order to provide audibility for the speech from the left and from behind, and the right aid in a directional polar pattern to give directional benefit for the speech coming from the front.

Signal to noise ratio required for 50% correct speech discrimination is shown in the bar graph. The lower the value the better.

When the target speech was directly in front of the subject, brand A and B products had a small advantage over ReSound LiNX 3D due to their binaural beam forming technology. Binaural beamforming is only optimal if the target speech is coming from the front only.

However, in the “real” world the speech of interest is not always from the front. In the graph below we see the result of Binaural Directionality III working to its purpose, namely providing audibility of speech from all directions. This allows the wearer the ability to change their focus to the speech of interest.

As products A and B are both still only focused on the speech in front, the wearer now needs a much higher signal-to-noise ratio to understand speech coming from their left side. In contrast, ReSound LiNX 3D provides significantly better audibility for the wearer’s signal of interest.

The graph below shows a similar result when the speech of interest arrives from behind the user. Again, ReSound LiNX 3D’s Binaural Directionality III shows a marked improvement over binaural beamforming products for hearing and understanding “off-axis” speech.

In conclusion, ReSound LiNX 3D's fully automatic Binaural Directionality III provides the wearer the ability to detect and focus on speech signals arriving from any direction. This is in contrast to binaural beamforming technology which makes assumptions about the wearer’s listening intent. Binaural Directionality III is a directional solution optimised for “real world” listening situations.

Michael Stockhammer
ReSound. Senior Area Manager, North Island NZ