Better Signal Processing

This is the first part of my wishlist to audiologists and accousticians, hearing aid manufacturers, and the health care system. If you like to add something, share your experiences, or provide more information, I encourage you to submit a comment.

Nowadays hearing aids still don’t fully compensate a hearing loss. They fail particularly in difficult but frequently occurring acoustic situations. The reality is that the cocktail party problem still exists and that it makes life hard for the hard of hearing. Hearing-impaired people still avoid noisy situations like in restaurants, bars, at parties, or any kind of event where a lot of people are talking. Since those are exactly the situations where people socialize, hearing-impaired people have significant problems in connecting to other people – both in their personal life as well as in professional environments. That means if you are not able to make friends and business partners, you will get isolated and won’t make a career.

Also, many hearing-impaired people depend on lip-reading and ‘guessing from the context’, because hearing aids are just not good enough. It is not uncommon that hearing-impaired people still avoid situations where they have to rely on acoustic channels and switch to workarounds like subtitles for movies or text messaging instead of calling on the phone.

One specific problem of the signal processing of hearing aids are feedback loops. Feedback loops occur frequently when something is close to the hearing devices, for example if you put on a hat, if someone hugs you, or you lay down on the sofa to watch a movie. The only effective measure that today’s hearing aids have is to detect the feedback loop and then damp the affected frequencies. But those frequencies might be the ones that you need to understand speech. Thus, you have the choice between wearing a hat on a cold winter day or being able to understand the person in front of you.

See also the next point on my wishlist: Compatibility between vendors for hearing aids and peripheral hardware.

4 thoughts on “Better Signal Processing

  1. Is there any way to monitor (even after the fact) if my hearing aids are dampening frequencies to avoid feedback loops? It would be really handy to be able, in a given situation where I have the impression I’m not hearing the person I’m talking with too well, to be able to know if frequencies (and which ones) are being cut out by the anti-larsen.

  2. The only way I know of is the fitting software. At least the one of Siemens has a real-time monitor where you can see what is amplified (or not) in exactly that moment. I would assume that you can see the damping there, but I am not 100% sure if I tried that so far.

  3. I am an audiologist. I can’t imagine how life is with a hearing loss because I still have normal hearing however I see hundreds of clients each year who do so I do have some experience on this subject.

    I’m sure this has been explained to you however your problem in noise/groups/crowds/cocktail parties has less to do with your hearing aid and more to do with your hearing impairment. It is extremely difficult for any type of digital signal processing to accurately separate two similar voices in a sea of other voices – even people with ‘normal’ hearing cannot do this and look to other cues such as lipreading and guessing. On top of that at the end of the signal chain you are presenting sound to a damaged system. I test people’s ability to understand speech in the best possible conditions – quiet sound treated rooms, isolating headphones with the words at high volumes of presentation directly into their ear and if they have a severe hearing loss they typically only get 60-70% of the words correct. If in the best possible acoustic situation with only one voice the baseline hearing is only 60-70% there is no way that any technological solution will make them do any better in noisy crowd situations.

    The typical signal processing available in hearing aids does not really improve hearing in noisy situations – it is there to dampen (not remove) what the hearing aid thinks is background noise to make the sound quality more comfortable and that you don’t go to pull it out or turn the volume all the way down. The only feature that improves hearing in noise is the microphone and the more directional it is the better the hearing in noise and soon hearing aids will all have twice the directionality of the previous generation of hearing aids due to a breakthrough in wireless transmission of sound between left and right hearing aids, however this will only reduce noise from behind by 6dB which for some people is still not enough to make a significant difference. There are FM systems which will reduce background noise by up to 25dB however you need the person who you are talking to to talk into a microphone – not many hearing aid users I see are willing to use this because it requires too much effort or they don’t want to impose this very good solution onto other people.

    In this age of technological solutions it is very easy for us to place the burden on technology to fix our problems because it already does so much for us. However when technological solutions are still reliant on residual function at the end of the day a signal chain is only as good as it’s weakest link. For all hearing aid users the weakest link is almost always the hearing system it is being connected to.

    PS. if you want less feedback choose a behind the ear hearing aid that blocks your ear. The signal processing that hearing aids apply to reduce the chance of feedback/whistling can drastically reduce the sound quality, so the less of it being used the better. If feedback is a problem and you have an open fit style device you should ask your hearing specialist to try a custom tip/mould piece that is shaped to your ear; recent research suggests the more your ear is blocked the better the sound quality and performance of the microphones. However you will then have a problem of hearing your own voice more! One problem solved causes another, such is the compromise of the hearing aid.

  4. I couldn’t agree more with David Audiologist’s post above. We often expect technology to solve all our problems. In the end, it’s the software of our bodies that has it’s own limitations which might never be overcome!

Leave a Reply