Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!wuarchive!udel!bunnell From: bunnell@udel.edu (H Timothy Bunnell) Newsgroups: comp.dsp Subject: Re: DSP Hearing Aids? Message-ID: <33682@nigel.ee.udel.edu> Date: 17 Oct 90 01:56:38 GMT References: <1990Oct16.163935.1954@ux1.cso.uiuc.edu> Sender: usenet@ee.udel.edu Organization: University of Delaware Lines: 52 Nntp-Posting-Host: dewey.udel.edu 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