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There is a feedback elimination process when they tune the hearing aid using the computer. It tries to work out what feedback is escaping, to cancel it.  But wearing it, sitting still in the audiology room is different to real life when there is more movement creating further feedback. Hence feedback still being an issue.  I'm guessing the processor in the hearing aid itself doesn't monitor for feedback, there's only so much you can fit into a hearing aid before it gets too big.

Perhaps headphones take away the filtering abilities because you lose the ability to judge direction and distance?

by In Wales (inwales aaat eurotrib.com) on Fri Aug 31st, 2007 at 02:33:47 AM EST
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If there's a one-off feedback elimination pass the digital signal processor in the aid probably has what it takes to do adaptive feedback elimination.

I'm curious about what algorithms are being used. There's a lot of hands-on experience in music and audio engineering of eliminating noise and increasing perceived volume. I have a depressing feeling that audiology is off in a separate world, and the two disciplines aren't talking to each other as much as maybe they could be.

That's a good point about headphones, because the folds around the ears physically steer sound and add directional information that won't be picked up with a point microphone or reproduced with a pair of point headphone speakers.

You can fake the effect using either a plastic head with fake ears (it looks odd, but it works surprisingly well) or mathematically using something called a Head Related Transfer Function. (Great name...)

I suppose potentially you could improve noise filtering by increasing the effect of the HRTF. You'd get more directional hearing - which wouldn't always be useful, but could be an improvement in some situations.

(Just speculating...)

by ThatBritGuy (thatbritguy (at) googlemail.com) on Fri Aug 31st, 2007 at 10:17:32 AM EST
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An interesting point about potential overlap of audiology and music/audio engineering.  I've no idea at all how much information and experience is shared in developing digital aids.

I'm far more seeing the privatised aspect of the field of audiology creeping in, with adverts all over the waiting room, and all reading material aimed at buying aids and accessories.  I'd assume that technology development takes place within these companies in a fairly closed way.

I'd love to see one of those fake heads!

by In Wales (inwales aaat eurotrib.com) on Fri Aug 31st, 2007 at 10:34:21 AM EST
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Here's a home made version.

And here's a commercial (if that's the word...) binaural mike system:

Dummy head recording gets rediscovered as a fun thing to do every ten years or so. Apparently Pearl Jam used one on a recent-ish album.

by ThatBritGuy (thatbritguy (at) googlemail.com) on Fri Aug 31st, 2007 at 10:58:35 AM EST
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Smart! Thanks!!
Surely it would need some piercings to be cool enough for Pearl Jam?
by In Wales (inwales aaat eurotrib.com) on Fri Aug 31st, 2007 at 11:04:32 AM EST
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Must...not...Photoshop...
by ThatBritGuy (thatbritguy (at) googlemail.com) on Fri Aug 31st, 2007 at 12:27:59 PM EST
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my 91-year-old massage client has one of these, and when i lean over and give her a kiss, all hell breaks loose...sounds like a kitten yowling.

i don't understand why!

great diary, thanks in wales-

'The history of public debt is full of irony. It rarely follows our ideas of order and justice.' Thomas Piketty

by melo (melometa4(at)gmail.com) on Fri Aug 31st, 2007 at 05:16:52 PM EST
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That's feedback!  It happens when anything gets too close to the microphone of the aid.  What are you doing with these clients of yours???
by In Wales (inwales aaat eurotrib.com) on Fri Aug 31st, 2007 at 05:37:10 PM EST
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i know it's feedback, i just don't understand why me leaning over her and bringing our heads together makes it go off.

i'm just a person, not a mike or a speaker.

and no, i don't usually kiss my clients.

when i get to know someone really well, they become 'frients'

i can't help it with her tho', and at her age she doesn't have to worry about darker motives!

'The history of public debt is full of irony. It rarely follows our ideas of order and justice.' Thomas Piketty

by melo (melometa4(at)gmail.com) on Sat Sep 1st, 2007 at 01:42:33 AM EST
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