Where is technical hearing aid info available?

I now need hearing aids. Getting is even crazier than seeing an optometrist to get glasses. Blaming proprietary information, I have not
been able to find out any detail about just what digital hearing aids can do. I have no list telling me what the algorithms can do. so that I can ask for a particular program. It should not be that complicated.
Some of what I want to know is
1. How can two microphones a centimeter apart (if that much) be used to get directional behavior as claimed. At 343.2m/s, the phase change for 1000Hz is only 0.03 wavelengths. How can that be processed to provide a directional microphone behavior?
2. Can I get a program to clip or limit short bursts of sound such as clanking dishes? My observation is that the pulse of noise comes along and comes through loud. What follows, speech that is the signal, get reduced gain to protect you agains loud sound that is already gone.
3. Covering one of the microphones with my finger improves the quality of sound by extending the band to include sibilants. Why cannot the hearing aid program do that?
Any clues as to where useful information exists on the web or in a reasonably priced ebook would be appreciated.
--

Sam

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On 01/29/2014 12:20 AM, Salmon Egg wrote:

Hello, and I initially tried to do the same thing for my 96-year old father. He had a pair of 6-year old Widex aids that didn't match his current level of hearing. At first I thought we would have to replace them and, being an EE, I began a search for the type of info you desire. What I found was a dearth of technical info online except for a few spec sheets and user's manuals from some manufacturers. (I think they treat their mantech they way Coca-Cola guards their original formula.) I've seen the module in my father's in-ear appliance and it's incredibly tiny.
I found out my father's Widex aids were capable of being reprogrammed and since they were in good operating order I had this performed by an audiologist who used a PC with appropriate software and an interface which connects through the aid's battery compartment. The audiologist used an audiogram that my father had done by his ENT doctor's staff audiologist. The reprogramming fee was a fraction of what new aids would've cost. (Technological advances after 6 years certainly find their way into hearing aids. but I don't think my dad would have derived any benefit from a newer model, which was also the opinion of the audiologist.)
The biggest shock, if you haven't gotten it yet, is the price. Unlike glasses, the hearing aid market is tightly controlled. Many audiologists, while competent, are also dealers for one or more manufacturers. That isn't necessarily bad but one should be aware. It's certainly convenient if you're looking for a one-stop type of service. Most hearing aid dealers will honor a current audiogram performed elsewhere. A good place to start is with an ENT doctor who has an audiologist on staff That way you can get your ears examined medically (nerve damage, etc) and then do the hearing test at the same location. You also want to get possession of the audiogram.
Finally, I wouldn't scrimp on "cheap" (believe me that's a relative term here) hearing aids. OTOH, you may not need all the features of a super deluxe model. Manufacturers such as Widex, Phonak and Siemens all produce a wide range of high-quality models. Oh, and one other thing - be prepared to change batteries frequently. Good luck. Sincerely,
--
J. B. Wood e-mail: arl snipped-for-privacy@hotmail.com

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It was a pleasure to see your post.
A friend of mine has an ENT sib-in-law who he thinks is pretty good, but will not get hearing aids from his office audiologist. He is running into problems as mine.
At this timer, I would just like to get a list of what the bells and whistles can do for me. even that seems unavailable. I got my hearing aids at Costco. I am beginning to think that the dispensers, if they knew everything they should to be competent, would find more lucrative work.
Simple diagrams showing parts such as microphones etc would be a big help. Why does placing a finger over a microphone improve the intelligibility? I cannot even find out if they use FFT. I think so, because steady tones seem to be off key.
I googled DIY hearing aids and found a number of sources for hearing aids and programers. In desperation, I might go that way.
Anyhow, I will keep on looking and getting more frustrated.
--

Sam

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On 01/02/14 13:29, Salmon Egg wrote:

Silicon Chip ran an article on such recently.
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Salmon-
I don't know about hearing aids, but it works for telephones in a noisy environment. Placing fingers over the mouthpiece reduces background sounds that are fed back to the earpiece as "sidetone". (Sidetone is the percentage of your voice that goes back to the earpiece to let you know the phone is working.)
Fred
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I was thinking about that and asked the last person who fiddled with my hearing aids about side tone. He, of course, did not know what sidetone was.
Although sound although sound is a longitudinal (scalar) pressure wave in the air, the theory has much similarity to that of antennas. I have never heard talk of multipath problems with hearing aids. I do not understand how two small microphones space a small fraction of a wavelength apart can be processed to give directional patterns. U can understand that spacing BETWEEN ears can give rise to interferometric cues. When I asked if the two aids exchange audio information, the answer was no.
--

Sam

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On Sat, 01 Feb 2014 16:52:23 -0800, Salmon Egg

We've been working with phased microphone arrays recently. It was amazing to see that the recommended spacing for one solution was 11mm. You're right, it doesn't make much sense, given common knowledge of antennas.
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wrote:

You would think that it would depend upon the frequency. I would be very surprised if there were no experiments listed in the literature that looked into how well the stereo effect was sensed as a function of frequency.
Becaus sound is longitudinal. could it be that hearing aids process amplitude rather than phase for directional discrimination? I can picture two microphones angled with respect to each other with a difference of transduced amplitude because one is hit normally by the sound while the other is hit obliquely. It is sort of like the dependence of illumination of a surface being affected by the angle of incidence. Think Lambert's law.
--

Sam

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On Sun, 02 Feb 2014 19:26:19 -0800, Salmon Egg

Yes, frequency dependence seems natural. These are audio frequency microphones, 20-20K, so we're talking about a *lot* less than a wavelength.

Nope. These microphones are coplanar.
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On 02/02/14 08:52, Salmon Egg wrote:

The "All singing dancing" models now communicate with each other and everything else too.
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