The holy grail for digital hearing aids is to allow wearers to hear speech more clearly in the presence of background noise. So whilst modern hearing aid manufacturers claim to use noise reduction technology - does it actually work?!
‘Noise’ simply put is sounds that we do not wish to hear. This can be anything from the hum of a refrigerator, traffic (cars and planes), wind, doors slamming, road works, and worst of all … the background babble of many people speaking (know as cocktail party noise).
Background noise can typically be split onto two forms - that of steady state repetitive low frequencies such as air conditioning and traffic, or noise which is more random and intermittent such as plates clattering, cutlery being sifted through or heels on hard floors, and these are typically higher in frequency.
Digital technology allows us to manipulate incoming sounds at extremely fast rates before transmitting it to the wearers ears. The technology used includes:
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Low frequency roll off
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Noise reduction / NR- reduction of repetitive low frequency noise
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Sound Smoothing – focusing on suppression of sharp loud sounds to a comfortable level
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Directional microphones – reduction of sounds from behind (or other direction)
The key to all these forms of noise reduction is to reduce unwanted sounds without impinging upon the clarity of speech, and more specifically the actual person we want to hear speaking.
1. Low frequency roll off
Being that a lot of background noise is low in frequency, some programmes may reduce the amplification of the lower frequencies and give a slight boost to higher frequencies in order to enhance the ‘clarity’ of words which are higher in tone.
Does it work? – Low frequency roll off does give some assistance to making it easier to focus on the clarity of speech for certain people, but it is not enough on it’s own.
2. Noise Reduction / NR
NR focuses on trying to reduce steady state / repetitive waveform noise. NR is simple to achieve when speech is not present as we can just reduce the interfering sound. But when there is speech present we have to try and reduce the parts of noise in between the speech signal without hindering that speech signal. In order to do this the microchips have to work VERY fast between all sibilants of speech and act upon what it considers to be noise. Of course a hearing aid doesn’t actually know what is noise and what isn’t – the programming is set to recognise different waveforms, but as these overlap it is very difficult to remove all noise, and more so to do it without having some effect on the speech that is present. Some hearing aids incorporate speech enhancement technology in the higher end models to really try and bring out the best of NR.
Does it work? – It is impossible to incorporate NR without impinging on the gain for the speech, thus noise reduction works well for some and not so well for others. Noise reduction can act more as a comfort control which makes listening to speech in noise easier.
3. Sound smoothing
Sound smoothing is a feature that most leading suppliers now use, but this feature may be called a different name such as ‘sound relax’ or ‘anti-shock’.
Sound-smoothing technology is a very quick acting compression feature that dampens sharp impulsive noises. We have engaged this feature many times for clients who have sensitivity to loud sounds such as plates clattering and they have commented postiviely on he difference.
Does it work? – Yes. Very effectively for most people who would benefit from it.
4. Directional Microphones
Most modern hearing aids incorporate dual microphone technology, with the exception of the smallest in-the-ear hearing aids called CIC’c. Dual microphones simply means each hearing aid has two microphones – these microphones work in unison with each other and using the latest computer algorithms have the ability to focus on sounds in different directions (generally in front as we face the person we speak to). Directional microphones will be dealt with in more detail in a later lesson.
Does it work? – Yes. Dual microphones work, but they naturally work better in test environments which are carried out on dummy models in anechoic chambers where sounds are absorbed. BUT… In reality sounds bounce off walls and this makes dual microphones less effective in closed environments.
Below is a video link that shows dual microphones do work, but note in an open field environment where sounds can’t bounce around.
Video Link
Most hearing aids are now fully automatic – meaning automatic volume control to suit the wearers hearing loss and upper loudness levels, and they incorporate up to 4 programmes switching automatically between each other depending on whether speech or noise is present. (3 typical automatic programmes being quiet, speech in noise and noise only).
For noise reduction to work we need to incorporate all the above featuresinto these automatic programmes so that they work together. We can also set up additional programmes and turn these features up a notch which does help many clients.
Wearers of hearing aids must remember one crucial point – if you have a hearing loss result and from nerve damage to the inner ear, then your hearing organ is damaged – therefore we are sending an improved signal to damaged hearing and you may never get the clarity you desire because of this.
Microchips currently work at up to 400 million calculations per second, and are getting faster and more powerful every year which means hearing aid technology is always getting better, but we are still sending this improved technology to damaged hearing and this will only ever be overcome when we can replace or repair the nerve damage.
We will also do an article on FM hearing aid solutions soon which can be a boon to peoples lives.
