The holy grail for digital hearing aid developers is to allow wearers to hear speech…
This Lesson is now outdated somewhat as hearing aid manufacturers have increased the number of channels in their hearing aids – Oticon (64) and Siemens (48).
Hearing aid channels are often misconstrued as something like TV channels. i.e. if we say a hearing aid has 10 channels, many people think this means we can turn the hearing aid to 10 different settings – this is NOT the case!
Hearing aid channel’s are frequency bands. Digital hearing aids amplify a frequency range of about 125Hz to 8000Hz. Hearing aid channels allow us to split this wide range of hearing into narrower bands thus giving the appropriate amount of amplification at each frequency tested across a hearing loss curve. This is more critical for sloping hearing losses, and especially so for steeply sloping losses.
The diagram below show’s the frequency range being divided up by a 4-channel hearing aid:
You can see how it gives a varying amount of amplification across the range. But it isn’t perfect as either side of a specific frequency will be giving slightly too much or slightly too little amplification.
The diagram below shows a 15-channel hearing aid, and you can see how the bands are narrower and therefore match the curve better:
Studies have shown that more channels are better, but also that once a hearing aid has more than 8 channels, the relative benefit is reduced dramatically. As such it is debatable as to what the best upper limit is for the maximum required channels. So whilst Oticon take the view that 10 is sufficient for their top-end hearing aids, the likes of Phonak and Unitron have up to 20, and Resound stick to 17 whilst Widex have 15. So is 20 too many? We don’t know, but it’s unlikely it will have a negative affect. But by the same token, don’t be fooled into thinking 20 is necessary. There are other features in a hearing aid that have to work in unison with each other to give maximum performance.
Most hearing aid manufacturers have 4 levels of technology in their hearing aid portfolio. And they increase the number of channels at each level. It is not critical if a hearing aid has 10 or 12, or even 15, but studies have shown that there is significant benefit as the number of channels are increased from 1 to 2, to 4, to 6 and then the relative benefit tails off.
It is important to consider what else is happening though. Advanced digital hearing aids have other features such as noise reduction and directionality. The two keys features for hearing speech in noise.
Noise reduction: basically reduces steady state background noise such as air conditioning (basic aids may reduce speech slightly too acting more as a comfort control, but more advanced aids retain the level of speech cues via speech enhancement)
Directionality: gives emphasis on sounds from the front, or for more advanced aids, give surround sound focus on speech.
The more basic hearing aids will only apply the above to the full amplified range (125-8000Hz)
The more advanced aids will apply these independently to each frequency channel. And the level of benefit is enhanced as the technology (and the price) goes up!
So ultimately, the number of channels gives an idea as to the level of technology, but as all manufacturers have their own idea as to the required maximum, you need to look at the other features offered to decide what is best, and as there are 8 major suppliers offering 4 levels of technology, with 4 or 5 different styles, and several other alternatives, you also need to allow some guidance by your qualified Hearing Aid Audiologist.
Please feel free to add comments or ask questions, or request a topic for the next lesson.
Thank you for reading this and joining in.