> I was thinking about noise canceling at the source (microphone). Many
> cell phones do this already with multiple microphone and they do it
> well.

Yes. There can be some very complex stuff inside consumer level
equipment. That may not be so, but can be and quite invisibly. eg

- I'm told that the best noise cancelling Bluetooth headset available
will literally blank out an adjacent chainsaw. I'm told that you can
here a chainsaw started up besides the wearer and then it just fades
away to inaudibility. Apparently not so good for music though.
(Guessing only: presumably the environmental adaptation tends to
prevent a consistent channel model.)

- Hearing aids used to be simple amplifiers with appropriate frequency
shaping and some clipping. Nowadays the best in ear ones are tiny but
reportedly have  DSP capability with tailoring of response in multiple
frequency bands and much more - and are remotely programmable.

Some of the hearing aid techniques may be applicable to your requirement fw=
iw.

Digital Hearing Aids: Current "State-of-the-Art"
http://www.asha.org/public/hearing/treatment/digital_aid.htm

SIGNAL PROCESSING TECHNIQUES FOR A DSP HEARING AID
Multiple microphones and noise cancelling mentioned in this pper.
Nothing very technical.
                    http://brent.edwards.name/Papers/TAA11_7.PDF

Digital Signal Processing and Hearing Aids
2002 - "everything has changed ...
               http://www.healthyhearing.com/articles/7719-digital-signal-p=
rocessing-and

A DSP implementation of a digital hearing aid with recruitment of
loudness compensation and acoustic echo cancellation
Sounds highly apposite - abstract only but you may have access via
yoiur institution.

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=3D625579

Digital Hearing Aids - the Way of the Future
http://www.digital-recordings.com/publ/pubaids.html

Gennum Abandons Hearing-Aid Market With DSP Chip and Headset Spinoffs
2007. Interesting if not overly relevant :-)
http://p6.hostingprod.com/@hearingmojo.com/blog-mt/blog-mt/2007/09/gennum_a=
bandons_hearingaid_mar.html
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