- Dec 5, 2019
Channels and Bands
Hearing Aids are designed to enhance the sounds coming into your ears making them clearer, with more volume or gain.
The significance of smaller more powerful hearing aids increases the capabilities of the hearing aids to improve your experience.
In this article we will discuss how hearing aids work, the use of Channels and Bands interacting with other features like digital noise reduction, feedback suppression, and multichannel directionality.
"a hearing aid channel will be defined as a range of frequencies that is created by a digital filter or series of digital filters within the hearing aid. In addition to expansion and compression, most signal processing features such as digital noise reduction, feedback suppression, and multichannel directionality operate on a channel-by-channel basis. Bands will be defined simply as the number of adjustment "handles" provided in the programming software for gain manipulation."The Value of Increasing the Number of Channels and Bands in a Hearing Aid
A Band is described as an adjustment handle within the hearing aid software for gain manipulation.
If there is a processing delay of more than 3 to 6 msec, this may be noticable to the hearing aid wearer. Increasing the Channels increases the processing requirements of a hearing aid. When the processing cannot keep up, there is a difference in what your ear may naturally hear and the sounds enhanced by the hearing aid. Often a hearing aid wearer will have normal hearing at some frequencies, and loss in other frequencies. A high tone loss will impact your ability to hear parts of words. Refer to Understanding an Audiogram
This may be noticed as a slight echo.
"Frequency-specific group delays" is a technical term referring to the processing delay difference for lower tones compared to higher tones. Having more channels increases the delays.
The number of Bands in your hearing aid, affects the audiologist's ability to configure the hearing aid's frequency response.
For people with steeply sloping losses (eg you have near normal low tones and a steep drop off in mid to high tones), a greater number of adjustment bands is required. So the outcomes are affected by your hearing loss and the level of hearing aid you purchase.
Now imagine the complexity when you have a different hearing loss in your left or right ear. In these situations you need an experienced audiologist to test, fit and program properly, with a knowledge of both hearing aids and the accessories and apps you can combine them with.
Your hearing aid can only be as effective as the original testing allows.
Your Brain and your Hearing Aids
Your brain adjusts to your hearing aids, refer to our article Auditory Deprivation & Brain Deterioration ...
"The term 'auditory deprivation' refers to a person's lack of adequate hearing stimulation."
The great news for people suffering hearing loss is the dramatic increase in processing speed of modern digital hearing aids.
This increase in processing speed is also matched with new rechargable battery technology and wireless capabilities.
Widex discuss the downside to a multichannel hearing aid
"having multiple channels increases the risk of spectral and temporal smearing, which is a reduction of the contrasts between the peaks and valleys within the speech signal"Widex
The page also explains that those with severe hearing loss need contrast for proper speech identification.
Widex also suggest you look beyond the number of channels-:
"While the number of channels is definitely a deciding factor in selecting a hearing aid, how the hearing aid handles potential smearing, along with the other signal processing algorithms within the hearing aid are also important considerations."Widex
Hence hearing centres with experience across Hearing Aid Brands in Australia are an advantage.
There may be a brand and style best suitable for your hearing loss.
Summary Bands and Channels
Hearing Aids have features that improve the understanding of speech including noise reduction and directionality.
Various manufacturers have a preference for different numbers of channels with studies showing that after 8 the benefit levels out dramatically.
So just what is a channel and band?
If you look at your hearing chart you will notice it plots your hearing level across various frequency ranges.
These frequency ranges start at 125Hz until 8000Hz.
Hearing Aid Channels split this wide (normal) range of hearing into narrower bands thus giving the appropriate amount of amplification at each frequency tested across a hearing loss curve.
Hence a more technically advanced aid will have numerous channels to give varying amounts of amplification at different frequencies.
A Band is what is used to control volume in different frequencies.
An advanced hearing aid may apply noise reduction to different frequencies in response to the environment.
Say for example you were next door to someone using a drill - an advanced aid may notice the sound and direction of that sound and pick it as non speech (steady state background noise) it may reduce the volumes at various frequency ranges to reduce the effect of that noise to the user.
A simpler aid would not be as precise at achieving this.
More recently, frequency-specific directionality has been introduced in hearing aids. In this mode the hearing aid uses the output from the directional microphone over part of the frequency range (usually the high frequencies) and from the omni-directional microphone over another part of the frequency range (usually the low frequencies). While this compromise is not as efficient at improving speech understanding in noise, this particular implementation that causes the spectral shape of a sound to vary with the arrival direction of sound may enhance the ability of the wearers to localise sounds.
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