3D sound for hearing aids | EOS Science
Thanks to your ears you hear Three-dimensional: Since your ears work together, you can tell where the directional sounds come from. How does this work? Imagine a sound coming from the left. This sound comes a little earlier and reaches your left ear with more force than your right ear. Then the magic happens within Your ears: Your brain compares the difference in arrival time and volume between the ears to determine which direction the sound is coming from. Often this involves very small differences: for example, we can observe volume differences of less than 1 decibel, time differences of only 10 microseconds … that means one hundred thousandth of a second!
For example, by (subconsciously) focusing on the nuances of volume and time of arrival between the ears, we can learn the source of the annoying mosquito wheezing. In this demo, you can see how this works:
3D listening also makes it easier to distinguish between different simultaneous speakers because they are in different locations. This is especially useful when you want to focus on a single speaker in a noisy conversation, which is often unfortunately very difficult for people with hearing impairments.
Demo: If two speakers are in different locations, you can distinguish between them more easily, and thus better focus on one of them. With hearing loss, they are less able to perceive different locations, so such concentration is more difficult.
Hearing loss challenge
People with hearing loss often find it very difficult to follow conversations, and the impact of this cannot be underestimated. This can make them feel lonely and isolated in most social environments – for example with family at the dinner table or at a party with friends – and sometimes they avoid these situations.
Hearing aids really make a world of difference: they are amazing devices with the latest electronics and innovative algorithms. Unfortunately, at the moment they only take into account a few of the benefits you can experience from binaural hearing, and this is a missed opportunity. Hearing-impaired people are less able to “hear three-dimensionally”.
A new solution… an old technique
While studying for my PhD at KU Leuven (ExpORL research group), I researched new hearing aid algorithms to improve “3D hearing,” with the goal of facilitating conversations in noisy environments. The solution was surprisingly simple. I discovered that I – with slight modification – She was able to take advantage of the ancient technology found in almost every modern hearing aid: Directional microphones. A directional microphone picks up sounds coming from a specific direction, usually from the direction the hearing aid user sees. Thus, hearing with such a microphone is like looking at a flashlight in the dark, seeing objects only in the direction in which they are shining.
The directional microphones in today’s hearing aids assume that the user is only interested in sounds coming from the direction they are looking at. It is therefore set up to suppress all perceived sources of interference from behind and next to the hearing aid user. This is often a reasonable assumption, and indeed helps many hearing aid users understand speech in today’s noisy environments. Unfortunately, this setup does not facilitate “3D hearing” and can even be counteracted.
How can you “hear 3D” better with directional microphones? The solution I suggested is to rotate the direction of the microphones a bit: the device in the right ear will mainly pick up sounds coming from the right side, and the one in the left ear will do the same for the left. Now again imagine the situation in which the sound comes from the left: the left device will pick up that sound, and the right device will not pick up or hardly at all. This creates a much greater difference in volume between the two ears than the difference in round mics. Thanks to this difference in volume between the two ears, you can tell that the sound came from the left.
By turning the microphones slightly to the side, hearing aids allow you to better “hear 3D.”
The effect of the twisted mics turned out to be so great that it allowed a person who could not locate sounds using their hearing aids to do so once our algorithm was created. Further tests also showed that our algorithm can also help you understand speech better in noisy environments.
I think this solution can be applied and will be implemented in hearing aids in the near future, but this does not solve all problems. Unfortunately, the improved “3D hearing” we noticed wasn’t anywhere near what you’d expect from someone with normal hearing. A possible explanation is that the proposed algorithm only amplifies the volume differences between the left and right ear. An algorithm that can also improve the perception of latency differences would be another big step forward. Ultimately, we want every hearing aid user to be able to comfortably participate in all conversations with friends and family, with or without background noise.
Benjamin Dieudonné is competing for the 2022 Flemish PhD Cup. Find out more about this research at www.phdcup.be.
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