Path: utzoo!attcan!uunet!ogicse!mintaka!think.com!eplunix!raoul
From: raoul@eplunix.UUCP (Nico Garcia)
Newsgroups: comp.dsp
Subject: Re: DSP Hearing Aids?
Message-ID: <952@eplunix.UUCP>
Date: 17 Oct 90 15:08:32 GMT
References: <1990Oct16.163935.1954@ux1.cso.uiuc.edu> <33682@nigel.ee.udel.edu>
Organization: Eaton-Peabody Lab, Boston, MA
Lines: 34

In article <33682@nigel.ee.udel.edu>, bunnell@udel.edu (H Timothy Bunnell) writes:
> 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-

Hmmm. Why build a switched capacitor filter, or fancy processing for 
gain stage controls, etc., when straight forward analog ciruits will
do the job efficiently and compactly? It's only audio range signals anyway,
but it needs to be handled in real-time. Why ask for design sophistication
when you don't need it? 

I also had a fascinating conversation with an audiologist here about
different compression schemes. I won't go into details since I'm an EE, not
an audiologist, but one scheme that works surprisingly well is clipping:
map a 60 dB range speech signal into a 30 dB comfortable range for the
subject by clipping the upper 30 dB right off. Some guy called Lickliter
documented this technique in the 40's, and found that as long as the 
frequencies, relative intensity of them, and timing information was
preserved, speech was still comprehensible.

What it does to music, you don't even want to think about!

I believe that more effective processing for speech enhancement will
be based on what humans actually do, rather than what our mathematical
analyses insist is most efficient or powerful. I'm not certain, however,
that we understand enough of how people *hear* and process sound to 
approach speech enhancement from the speech production side.

Note: this is my personal opinion as an educated EE, not as an audiological
expert of some sort.

-- 
			Nico Garcia
			Designs by Geniuses for use by Idiots
			eplunix!cirl!raoul@eddie.mit.edu