hearing aids

Jochen Wolters jochenw at ikki.informatik.rwth-aachen.de
Wed Mar 22 08:03:09 EST 1995

dak at kaa.informatik.rwth-aachen.de (David Kastrup) writes:

>WELL... Digital signal processing is not yet employed in any hearing
>aid I know of,

I do know of at least one fully digital hearing aid (by Danavox, if I remember
correctly) .

>and fitting hearing aids based on the audiogram, as well as loudness
>adaptation in several bands, well, seems sort of basic.

Let's put it this way: the technology sure is basic, but, unfortunately,
a lot of hearing aid resellers still rely on the threshold method only. So,
even if loudness scaling as a means of hearing aid fitting is widely avail-
able, this does not mean that it is actually adapted to every day use.

>These things help, of course, but the advantages are strictly
>limited (you cannot gain more than 3dB SNR per doubling of the microphone

Please don't get me wrong, but so far I know of practically no patient
who cares about technical data. The goal of using hearing aids is to
improve the hearing ability of the patient with emphasis on speech
intelligibility, and not to develop some truely impressive technology,
although the latter may be required to persue the former.

The same obviously applies to multi-channel dynamic compression with IBI
(inter band intelligence, an algorithm that uses the control signal
of some of the frequency bands to influence those of others). The
properties of the signal do change (as seen in spectral and modulation
analyses) and one can clearly hear some difference, too. But the effect
on speech intelligibility for hearing impaired subjects is all but

>If you find that it is the only device that does so, this is not as much
>a compliment to this device, as a scorn for the others.

>The result, of course, is the same. People prefer using the best available,
>whatever or however that be.

...depending on the type of hearing loss and the intended use (noise conditions
etc.). And obviously, the Phonak device is great for patients with considerable
recruitment in background noise conditions. This does not imply, however,
that other technological approaches or other hearing aid models are inferior
to this very device.


Jochen Wolters - jochenw at POOL.informatik.rwth-aachen.de - cand.ing. EE 
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"You've never seen a picture of 'a picture is worth a thousand words.'
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