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110 plus decibels bellowing at my inattentive cochlea

Yow. No wonder that hurts.

Well, programme 2.  This is the real magic of this newfangled piece of technogadetry.  It cuts out background noise.

Reading this, I'm disappointed it has taken this long. Audio isn't rocket science and there are all kinds of clever things, from adaptive filtering and equalisation to echo cancellation to feedback elimination that should be standard issue on any audio processor.

The feedback is inexcusable. It's fantastically simple to design an audio processor that recognises and eliminates feedback. I have no idea why it's not included as a standard feature.

But this is interesting for other reasons. One of the problems with any kind of location recording is that what ends up on the tape and/or hard disk isn't what you hear when you're there. Normally the brain is good at prioritising certain sounds. So - e.g. - if you're listening to a busker, you won't hear people's footsteps, passing traffic, or other ambient noise.

It's always interested me that this changes if you use a microphone and a pair of headphones. For some reason this turns off the brain's filtering abilities and suddenly all of those ambient sounds become just as important as the 'target' sound.

The effect works whether you listen to a recording later, or through headphones on the spot. It would be interesting to know what's happening there. If you could somehow get the built-in filtering to work again, it might do something useful for hearing aid design.

by ThatBritGuy (thatbritguy (at) googlemail.com) on Thu Aug 30th, 2007 at 05:50:36 PM EST
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
[ Parent ]
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
[ Parent ]
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
[ Parent ]
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
[ Parent ]
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
[ Parent ]
Must...not...Photoshop...
by ThatBritGuy (thatbritguy (at) googlemail.com) on Fri Aug 31st, 2007 at 12:27:59 PM EST
[ Parent ]
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
[ Parent ]
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
[ Parent ]
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
[ Parent ]
Reading this, I'm disappointed it has taken this long. Audio isn't rocket science and there are all kinds of clever things, from adaptive filtering and equalisation to echo cancellation to feedback elimination that should be standard issue on any audio processor.

I disagree, actually. Battery life must certainly be a huge issue in a hearing aid when running a DSP, even an audio DSP that doesn't have to run at relatively high clock speeds. DSPs in cell phones have been around for about 8 years, and back in 1999, cell phone batteries were probably 100x larger than the tiny batteries you can fit into a modern hearing aid. As a rough guess I think a DSP in a hearing aid would have been possible about three years ago, primarily because ultra low power DSP's are a specialty device (ie, very low volume (no pun intended)), meaning the market doesn't get the same attention as the consumer electronics market, and when it does, I'd also expect the development time to be longer. That's also about the time that bluetooth audio devices came out which are a roughly analogous product with maybe half the complexity.

you are the media you consume.

by MillMan (millguy at gmail) on Fri Aug 31st, 2007 at 06:37:12 PM EST
[ Parent ]
Also, I have no idea which companies are developing the DSPs / software for modern hearing aids. It wouldn't surprise me, though, if the audiology field really is a bit divorced from the people that make these products as you implied in another comment. Even though there are a lot of people in the world with hearing problems, the market is tiny when compared to the consumer electronics and durable goods (cars, etc) markets. The basic critique of capitalist priorities applies.

you are the media you consume.

by MillMan (millguy at gmail) on Fri Aug 31st, 2007 at 06:44:18 PM EST
[ Parent ]

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