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Author Topic: Does anyone know about audiometric tests?  (Read 6798 times)

lyner

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Does anyone know about audiometric tests?
« on: 02/11/2008 11:02:48 »
My hearing has been dropping off (as have other bits) and I went for an audiometric test the other day.
All it consisted of was finding my threshold level of hearing over a range of frequencies and produced a 'crude' audiogram graph with about ten points on it.
This was, apparently, enough to produce a formula for suitable hearing aids.
It strikes me that a simple frequency response as an incredibly simple way of characterising  a complex sense such as hearing.
If you wanted to discuss the quality of a Hi Fi installation you would look at frequency response, power output, signal to noise ratio, linearity, impulse response and several other parameters before deciding just how good it might be.
How can the one test achieve anything significant? I know that our hearing is a very 'smart' process and it is possible that it covers most problems but I doubt it. 
Bearing in mind that the appointment (NHS) took the best part of an hour and will result in the selection and setting up of two quite expensive bits of kit, there seems to me that there is a high risk of them not doing what is required and the money being wasted.
Is this what you would get if you paid through the nose to have it done privately?

I must say, though, the audiology Dept. was very helpful and friendly and my appointment was arranged very quickly. So no complaints in that direction.


 

Offline RD

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Does anyone know about audiometric tests?
« Reply #1 on: 02/11/2008 14:10:21 »
The advantage of private treatment is that the latest digital hearing aids are available immediately.
Digital hearing aids are increasingly available on the NHS, but there may be a long wait...

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Waiting times vary greatly around the country but, according to the Royal National Institute for the Deaf (RNID), some patients are having to wait up to two years, which they say is completely unacceptable. The RNID fears that waiting times are likely to increase further, following the Government's recent decision to exclude audiology from the 18-week waiting time target for treatment.
http://www.saga.co.uk/health/healthyliving/bodymatters/digitalhearingaidsonthenhs.asp


The RNID offers an audiometric test over the phone...

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If you think that you, or someone you know, might have some hearing loss,
 why not take RNID's simple five minute telephone hearing check on 0845 600 5555.
http://www.rnid.org.uk/mediacentre/press/2008/deaf_awareness_week.htm

« Last Edit: 02/11/2008 14:17:27 by RD »
 

Offline Bored chemist

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Does anyone know about audiometric tests?
« Reply #2 on: 02/11/2008 14:39:53 »
It's true that if I were buying a HiFi I would want all those parameters specified, but the one that I would really notice if they screwed up is frequency response. Also I'd probably not pay attention to the fact that the microphones and, aprticularly, the loudspeakers that form part of the system have the biggest distortion figures.
Power output for a hearing aid is a matter of having enough oomph (not difficult as long as you don't mind changing the batteries) and a volume control.
A decent impulse response generally follows from a decent frequency response.
It's difficult to build an amplifier with a reasonably well defined frequency response unless you include lots of negative feedback. Once you do that, the amplifier is likely to be pretty linear. (That might not be what you want for a hearing aid- some compression might be a good idea). The distortions in the transducers are likely to be modeled as a frequenct response rather than anything else.
The S/N ratio is likely to be limited by the tiny little microphone as much as by the electronics.

If they get the frequency response right they have sorted out most of the problems as well as they are going to.
 

lyner

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Does anyone know about audiometric tests?
« Reply #3 on: 02/11/2008 20:48:26 »
I would take issue with  the idea that linear distortion, in the form of frequency response, is more relevant than non linear distortion. A bit 'muffled' or 'toppy' is far preferable to  'grittiness', cracking or cross modulation.
Many of the possible faults in an audio system are at least as likely to introduce non linear distortions as linear ones. My hearing is faulty and the impression is of distortion and not obvious colouration. I could be wrong in my assessment of the faults and I know that the signal processing in the Ear is very complex but I would really like to know how a simple HF drop-off can produce such effects as I hear in 'overload' conditions.
Impulse response is far from predictable from conventional frequency response. The modern rigid speaker cones may well have an indistinguishable swept frequency response from the old paper cones but their impulse (temporal) response has improved significantly and significantly improves reproduced sound quality.
This is essentially a question of psycho acoustics and complex signal processing and not 'simple' electronics matter.
That's why I posted it here. Some specialist knowledge is needed (with respect, as ever, BC).
Any ideas, Chris, for example?
Google hasn't helped me much.
 

Offline RD

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Does anyone know about audiometric tests?
« Reply #4 on: 02/11/2008 21:12:33 »
When cataracts are removed the person can perceive that everything has a blue tint (cyanopsia), this is because their brain has adjusted the colour balance to correct for the yellowed lenses they have had for years. The blue vision can persist for months until the brain adapts to the new colourless replacement lenses.

I suspect something similar will happen with hearing, the brain has probably attempted to correct for the for the loss of high frequencies and this adaptation could initially cause distortion to be perceived when a hearing aid is first used, analogous to the temporary blue vision after cataract removal.
« Last Edit: 02/11/2008 21:19:07 by RD »
 

Offline RD

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Does anyone know about audiometric tests?
« Reply #5 on: 02/11/2008 21:51:43 »
These are comments of hearing aid users on a BBC forum...

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So is hearing someone speak still sounding like a Dalek or are things settling down now?
I usually find i get the Dalek effect for a day or so before things settle down when i get a new set of hearing aids,
it is not uncommon !!!...

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You will find that over the next few weeks you will become used to the sound.
It is strange and your ear will take time to adapt to it and interpret what all the strange noises are.

http://www.bbc.co.uk/dna/mbouch/F2322274?thread=5401042&skip=0&show=20#p62932897
« Last Edit: 02/11/2008 21:55:45 by RD »
 

lyner

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Does anyone know about audiometric tests?
« Reply #6 on: 02/11/2008 22:23:22 »
Are there any other tests though and do advanced aids do any more than filtering and variable gain?
 

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Does anyone know about audiometric tests?
« Reply #6 on: 02/11/2008 22:23:22 »

 

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