🚀 go-pugleaf

In article <1990Oct16.163935.1954@ux1.cso.uiuc.edu> sinistar@mrcnext.cso.uiuc.edu (Jeff O'Hare) writes:
>Hi.  I was wondering if anyone has heard of any dsp hearing aids.  I was think-
>ing about it last night, and it seems like it could be a great idea.  Real-time
>digital equalization could maybe give users more natural hearing, correcting
>the natural degradation of the ear.  I have heard (no pun intended) that hear-
>ing loss of high frequences is complete loss.  Is this true, and if so, what
>is the approximate rolloff rate?  With the DSP, such possibilities as harmon-
>ization could be used to lower sounds an octave so higher frequencies could
>still be heard, just an octave lower.  Well, has anyone else thought about
>this, or seen any made yet?  How about some dsp chips small enough to fit in
>a hearing aid?  The 96002 is pretty large I think...
>	Jeff

There has been an enormous amount of interest in this area and a large amount
of research.  There is/was at least one device already on the market (but it
has not been well-received by clinicians as far as I've heard). There is
research on DSP hearing aids in progress at CUNY, at the Central Institute
for the Deaf, at the Research Laboratory of Electronics at MIT, and many
other places. Lots of different kinds of signal processing have been tried
including amplitude compression (hearing impaired people often have a very
restricted dynamic range below which they cannot hear anything and above which
things are painfully loud), spectral peak enhancement (amplifying only the
most important parts of the instantaneous speech spectrum via adaptive
filtering), frequency compression as Jeff suggested above to fit more of the
speech signal into the reduced auditory bandwidth, frequency dependent
amplification to compensate for the attenuation characteristics of the
hearing loss, and other schemes. To date, about the only one of these that
always seems to provide clear improvements in speech reception
for hearing impaired people is frequency dependent amplification. Some
amplitude compression is probably desirable (some of the time). The more
complex schemes have tended to give sort of spotty results--sometimes
promising, other times not.

What all this means is that so far the one clear advantage of DSP hearing aids
is their adaptability: the same piece of hardware can be programmed to the
needs of many different users quite easily (given the necessary programming
hardware). By contrast, analog hearing aids that shape the speech spectrum to
compensate for the loss of the wearer must be prescribed and built (or at
least tweeked) on a one-at-a-time basis.  While this is potentially an
important advantage, the economics of it have not worked out favorably yet.
Analog aids are and will probably remain much cheaper for some time.

Many people working in this area (including me) think that effective
speech enhancement schemes will probably be based on signal processing
that imitates what people do with their speech when they try to speak
clearly (as opposed to their ordinary casual speech). We just haven't
been clever enough to figure out how to do that automatically yet. Any
new ideas out there?

--
Tim Bunnell
<bunnell@udel.edu>