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Analogue
hearing aids have been around for decades; these conventional hearing
aids use more traditional technology and are still widely popular
due to cost effectiveness. The most basic analogue hearing aid has
a microphone which picks up sound waves and changes these waveforms
into electrical waves. These waves are then amplified and then converted
back into an acoustic signal by the hearing aid's receiver.
Any
manipulation of this analogue wave will produce an element of distortion
which may impede clarity when this electrical waveform is changed
back to an acoustic signal. This can interfere with speech perception
and create "unnaturalness" in the perceived performance
of the hearing aid. These aids also have the tendency to add the
same amount of amplification to all levels of sound intensity, this
can result in problems such as doors shutting, cutlery rattling
and toilets flushing being far too loud for the user.
Some
users of these basic analogue hearing aids comment that they either
provide too little or too much amplification to reach a comfortable
listening level for their particular hearing loss. As a consequence
they are forever turning the volume up and down on their hearing
aids.
As
a consequence to the above more advanced technology circuits were
incorporated into the analogue range. Through non linear or compression
amplification it became possible to limit the distortion of loud
sounds and background sounds to an uncomfortable level for example
by limiting the level of incoming or outgoing sound volume etc.
The resulting sounds are perceived as more balanced and natural
with a lesser degree of distortion than the more conventional analogue
aids.
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Digital
aids also have a microphone to pick up sound but rather than convert
the sound waves into electrical waves they are encoded as a series
of binary numbers that measure its pitch and volume at a given instant
in time. Basically they are bits of data that are manipulated by
a tiny computer inside the hearing aid. Processing the sound bit
by bit is much more precise and accurate than with conventional
hearing aids, certain details can be altered without affecting the
overall quality of sound. This unique technology separates the incoming
sound into bands and processes each band independently, separate
circuit paths are used to independently process different frequency
regions of sound i.e. they are frequency specific.
Overall this technology keeps sounds within a comfortable range
for the listener whilst maintaining a clear and natural sound quality.
It can automatically adjust to changing environments; hence in most
cases there is no need for a volume control. The true digital hearing
aid is also far superior to its predecessors in tackling background
noise. It is important to remember that it is not possible to eliminate
background noise, however they are able to recognise background
noise and maintain a better signal to noise ratio enabling the user
to hear speech better in that environment
Digital aids can be programmed by an external computer and adjusted
to suit the specific needs of each individual wearer. A further
advantage is that annoying 'whistling' is reduced.
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