Recent Articles
Microphone directionality in
hearing aids
A microphone is an essential component in all hearing aids. It picks up sound from within the environment and converts it to an electrical signal which can then be processed by the hearing aid. You may have heard that it is best to have directional hearing aids, and this article aims to explain what directionality is, and why it will benefit you.
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Cerumen impaction
Although cerumen (ear wax) impaction was discussed
in an earlier issue of our newsletter, it remains a popular topic in the
clinic. As we frequently answer questions on wax build-up, we thought it
was time for some revision.
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Ménière’s Disease
There are many different causes of hearing loss,
ranging from presbyacusis (aging changes) to middle ear disease (for
example perforations of the eardrum). In a previous issue of our newsletter
we discussed otosclerosis, the abnormal growth of bone in the middle
ear.
Read More...
Restaurants in Auckland
where are the places to be and be heard?
Many of our clients experience difficulty hearing
their friends and family in restaurants, bars and cafes. Contemporary
trends in architecture and design have led to restaurants becoming noisier than
ever before.
Read More...
Otosclerosis
Otosclerosis is the abnormal growth of bone in the middle ear. It usually affects
the stapes bone, which rests in the entrance to the inner ear (the oval window).
As the disease progresses, the stapes becomes fixated in the oval window and
this interferes with sound waves passing to the inner ear.
Read More...
Tinnitus
Tinnitus is defined as the perception of sound in
the absence of a source of sound outside of the head. The term tinnitus is
derived from the Latin word tinnire, meaning to tinkle or ring.
Read More...
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Hearing Articles
We will be updating this feature article
on a regular basis to keep you informed about hearing loss.
This is the beginning of a series of articles “getting
to know your hearing instruments – inside and out”.
Signal processing in hearing aids
Signal processing can be described as what happens inside a hearing aid after a sound has been detected by the microphone, and before it is delivered to the receiver (or loudspeaker).
You may have heard of analogue and digital hearing aids and wondered what that
really meant. In basic terminology, the difference between the two is whether
the signal processing is carried out by electrical components or by digital signal
processing. The difference could be likened to a stereo that has simply a bass
and treble to adjust the sound (analogue aid), or whether it has a graphic equaliser
where many components of the sound can be changed (digital aid).
Analogue Signal Processing
In an analogue hearing aid the signal received by the microphone is modified by electrical components such as capacitors and resistors before passing to the amplifier and being heard by the wearer.
Audiologists controlled the output of these hearing aids with a small screwdriver that turned a trim-pot. The adjustments were limited to perhaps how much low or high frequency power was relayed to the client, and in some, the maximum output of the hearing aid. Analogue sound is like receiving a photocopy, and it causes deterioration of the original signal.
Digital Signal Processing
In a digital hearing aid, the sound still has to go through the electrical components
of the microphone and the amplifier, but the way in which the signal processing
is carried out is digital.
Once the sound is received by the microphone it passes to an analogue to digital
converter. This means that the analogue sound wave is converted into a digital
signal, ie 1’s and 0’s. Once the signal is digital, it is processed, the passes
through a digital to analogue converter, onto the amplifier, and then is heard.
Depending upon the hearing aid, the digital signal is broken up into a number of frequency bands. In each of these bands a number of changes can be made to the digital signal. So, for example, in one of perhaps 20 bands a signal can be modified to provide different outputs for soft, medium, and loud sounds! It can also be told to respond differently depending upon the sounds present in adjacent bands. A typical digital hearing aid is really a very sophisticated and miniature computer that makes millions of processing decisions every second, and still delivers a sound that appears to be in real time.
If you would like to print out this article click
here to download the pdf version - 64kb
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