[analog31]

It seems to me that a simple way to eliminate the feedback issue is to separate the microphone from the speaker. Hearing loss runs in my family, so I've watched my relatives struggle with hearing aids, and I've decided that when it's time for me:

1) I will build it myself and figure out the details, to hell with the audiologists and their racket.

2. I will carry the microphone and amplifier in my shirt pocket. No more feedback.

Ironically, with the advent of personal electronics, everybody wears some sort of gizmo on their body, so I think we could just persuade the elderly that hearing aids don't need to be invisible any more.

[Dwolb]

I'm not a hearing aid expert but the microphone and earpiece may currently be tightly coupled because it has to be. That is, human ears are very sensitive to phase shifts and time delays. Placing the microphone in a location that is not your ear may throw off your hearing somewhat (possibly ability to locate from where a sound originated).

[roberthahn]

I can vouch for this. I used to have an FM system - this is a mic that transmits on a very specific FM frequency to a receiver that's paired with my hearing aids. I loved it because I could easily use it to hear people near me in loud rooms, but it sucked in meeting rooms. The reason why is that I would hear someone speaking through my hearing aids and through the mic - at slightly different times. This is the phase shift Dwolb speaks of. This reduced clarity significantly.

That said, if analog31 wants to wear the mic on his shirt, that distance is actually good enough for most 1 to 1 conversations. Just understand that you're trading off "spatial perception" (no left/right balance if only one mic).

[ogig]

Short after losing one of my ears audition I was laying on a beach at the Mediterranean. Holydays, sun, good times. Then I felt a strong buzzing sound, it had to be a gigantic flying insect, so close to my head!. I jumped out of the towel and run some meters flapping arms around my head. Crowded beach and my own wife were perplexed at me and my flapping arms strategy did nothing for the sound that was still as loud an close.

Then my brain recalculated. Sound stopped and started again and the pattern was obvious then. I confused for some good 5-7 seconds a halfmile away boat siren with an insect around my head.

By first hand experience: It's amazing what the brain does triangulating the two ears input, and it is indeed very sensible to the quality of the inputs. On the other hand the brain is also great at adapting to new, lower quality sensors. I don't see that same scene happening now, after several years of one sided hearing.

My wife still recreates that moment from time to time.

[ricree]

Many modern hearing aids already have ways to do what he's looking for.

Bluetooth receivers for television or phones, for example. In other cases, I've seen lapel microphones meant to be worn by the person speaking.

If analog wants to build their own for the sake of the experience, or for cost, then I'm certainly not going to discourage them. But if all they want is the solution to that particular problem, it already exists and is being sold.

[Kluny]

As a hearing aid user: my spatial awareness (as provided by sound information) is pretty much borked anyway. If I can't see where a sound is coming from I have no way of knowing what direction it's from or how far off it is. Even a small amount of hearing loss can cause this problem.

[ramLlama]

Another advantage of having the microphones (yes, there can be more than one!) near the ear itself is for DSP. Many hearing aids use multiple microphones to selectively amplify sounds from the direction you are facing. I think this would work best with microphones near the ear, or at least in a known position.

[stefs]

definitely. binaural hearing is very important. a single microphone in your shirt pocket would be a bad idea and not even close to the quality of hearing you can get with current hearing aids.

[ramLlama]

A bigger issue with separating the microphone and amplifier is cosmetic: hearing aids sadly have a stigma attached to them and people are more likely to wear them if they are invisible. There is a reason why hearing aids are produced in hair colors.

Also, I found that the best way to get rid of feedback was to get an ear mold rather than using an "open-fit" mold. This is a clear separation between the speaker and the microphone and pretty much solves the problem in my experience.

EDIT: I noticed late that you addressed the cosmetic issue in your post. I don't see the elderly changing but our generation just might.

[randlet]

"I don't see the elderly changing but our generation just might."

I'm youngish (mid 30's) and recently had my hearing aids replaced and realized I had a strong preference to stick with fairly visible behind-the-ear units rather than something more "discrete". I want them to be visible so that people I'm interacting with will be more sympathetic about repeating themselves and may make an (possibly unconscious) effort to speak more clearly.

The line of thinking that got me over being self conscious was "Lot's of people walk around with assistive devices for their vision...why should I be embarrassed about the same thing for my hearing?"

[analog31]

If I notice that somebody has hearing aids, I make sure that they can see my lips when I'm talking.

[TheSpiceIsLife]

My first experience with a close friend who had partial hearing loss lead me to realise how much lip reading helped her. If she wasn't looking at your face her responses would often be nonsensical.

Also, I work in a noisy environment where hearing protection is mandatory, and I find I have less trouble understanding people if I can see their face.

[72deluxe]

That's very good reasoning. If a person with visual impairment walks around with a white stick, it's obvious and people normally cater for their needs. It shouldn't be any different with hearing.

What a good point.

I have an elderly friend who has suffered complete hearing loss in one ear after an infection and the other ear can only detect very very low frequencies, and he's constantly saying "PARDON?". It must be very difficult to hear ANYTHING going on, other than the rumble of lorries and buses. I wonder if they could put a pitch-shifting circuit in his hearing aid to shift sounds up/down so that they fall within his hearing range, whilst not shifting frequencies already in that range. That would help significantly, surely?

Just thinking out loud.

[jnbiche]

> I wonder if they could put a pitch-shifting circuit in his hearing aid to shift sounds up/down so that they fall within his hearing range, whilst not shifting frequencies already in that range. That would help significantly, surely?

If you read the article, you'll see that's more or less what most modern hearing aids do, via a technique called multi-band compression.

Edit: Actually, here anigbrowl, an audio engineer, states that this is not how multi-band compression works: https://news.ycombinator.com/item?id=8854142

Assuming he is correct, my above statement may well be wrong.

[72deluxe]

Multiband compression works by splitting the incoming audio into different bands, much like your bass/mid/treble controls on your EQ only works on bass/mid/treble parts of the frequency range. Compression is then applied to only those frequencies and then they are summed together.

There is no pitch shifting in multiband compression - pitch shifting involves moving the frequency up or down by a number of cents, semitones, octaves etc. It's the effect used to get the "chipmonk" voice (high-pitch and squeaky) where a normal voice is fed into a pitch shifter and it is shifted up or down. It is also how harmonisers work, where they work out the frequency you're singing at and shift it up 7 notes (or an arbitrary amount) so you can sing and get a harmony of yourself.

[jimktrains2]

> fairly visible behind-the-ear units

I've had hearing aids like that for almost a year, and "fairly visible" is a stretch; they're pretty blasé and don't stand out.

[randlet]

You're right, they're still fairly subtle and probably not the first thing someone would notice about me, but if I turn my head slightly, you're bound to notice my ear moulds/tube.

[jimktrains2]

True, I do wear glasses as well, so they kind of blend into that as well.

[ramLlama]

I too wear BTE's with glasses and most people are surprised when I tell them I wear hearing aids. They cannot see them.

This is especially true of modern "Receiver In The Ear" (RITE) models where instead of a tube carrying sound, you have a very thin wire going into your ear canal.

[thaumasiotes]

> hearing aids sadly have a stigma attached to them

It's probably worth distinguishing between two kinds of phenomena that might be described as carrying a stigma:

- Something might lead other people to mock or otherwise denigrate you for exhibiting it. Being fat is a good example here; fat people get a lot of messaging from society that they're worse people for being fat.

- Something might carry no real significance to the rest of society while still being viewed, by the individual, as painfully embarrassing. There's a traditional view that women don't like to wear glasses because they think the glasses ruin their looks. I don't know how well that currently corresponds to reality; I've known one girl who really hated her glasses for that reason and another who, not needing glasses of her own, liked to take other people's and wear them -- but that's the prototype of a "category two" stigma: a woman who hates wearing her glasses even though no one around her sees anything wrong with them.

I suspect that hearing aids are firmly within the second category, which means getting people to wear them "openly" should be doable.

[adrianhoward]

"I suspect that hearing aids are firmly within the second category, which means getting people to wear them "openly" should be doable."

You suspect wrongly. Having seen the attitudes to my father change when he wore one. Ranging from outright verbal abuse, to assumptions of stupidity & senility.

[hibbelig]

Maybe it's related to age? I've been wearing "behind the ears" aids since I was 7 and I never sensed any perception like that.

(I have no idea what is the correct term for "behind the ears", I hope it's understandable.)

[R_Edward]

17 years ago, I worked for a hearing aid manufacturer. The common terms in use there were BTE and ITE, for "behind the ear" and "in the ear." Frankly, I thought the initialisms were poorly conceived. ITE is three syllables, same as "in the ear," and less meaningful for the uninitiated. BTE only saves you one syllable, again at the cost of meaningfulness. But either which way, your terminology is both understandable and correct.

Off-topic: While I was there, they asked employees to submit ideas for a new hearing aid marketing slogan, with the incentive of a free vacation to Vegas going to the person who submitted the one they used. For some reason, I did not win the vacation with my suggestion: "Stick It In Your Ear!"

[thaumasiotes]

It would be pretty interesting to see people assume that a ten-year-old suffered from senility because he was wearing a hearing aid. By definition, it only applies to the old.

[72deluxe]

Really? Who from? That's terrible.

[adrianhoward]

Just people.

At the low end when eating out in restaurants occasionally having wait staff ignore him and asking other folk at the table "what would he like", or people assuming that he couldn't hear and talking about him — to at the high end having a guy shouting "deaf fuck" at him repeatedly on the street for no obvious reason.

I'm not trying to say that this happened every day — especially the outright insults. But it was enough to be noticeable.

I suspect, as @hibbelig commented, age had something to do with it.

[korethr]

While that sounds like a good idea at first, I think it makes sense to have the microphones at least near the ears.

The frequency content of a sound is directional, and moreso as the frequency increases. As a test, listen for a difference in the highs with your (computer/stereo/home theater/whatever) speakers both aligned with your ears, and not. Due to this directionality, a microphone in your shirt pocket would pick up a sound differently than one near your ear.

The brain does some very fancy and clever tricks based on the differences in the timing and phase of a sound as it arrives in both ears to determine things like relative position and distance. Having the hearing aid mics receiving sound similarly to your ears would should make it easier for the brain to continue to do these nifty tricks.

Otherwise, yeah, put the amp and other circuitry in your shirt pocket or wherever else is convenient. It should be a lot easier and cheaper to fit an amplifier and multi-band compressor in your shirt pocket, than in a tiny sliver of plastic that has to fit behind the earlobe.

[objclxt]

You can actually already get body units for hearing aids. Even better, you can get radio-aids, where the microphone is elsewhere. This is particularly useful for students in a classroom, for example, where the teacher may wear the microphone directly.

[mmmaaaxxx]

> 2. I will carry the microphone and amplifier in my shirt pocket. No more feedback.

This is how hearing aids used to be:

http://www.hearingaidmuseum.com/gallery/Transistor%20(Body)/...

[TheOtherHobbes]

>It seems to me that a simple way to eliminate the feedback issue is to separate the microphone from the speaker.

That won't necessarily fix the problem. Feedback comes from bad electronic/DSP design. Physical mic/speaker positioning makes certain solutions harder, but in practical designs it's not (usually) the limiting factor.

Phones of all kinds, Skype, etc include adaptive echo/feedback cancellation already. It's a well-understood technology - adaptive cancellation has been used since the 1960s - although the fact that it exists is maybe not as well known as it could be.

(Protip - if Skype starts feeding back, you can often reset the adaptive filter by clapping once loudly.)

As for hearing aids - the first papers mentioning multiband compression date from the 1980s, so there's nothing new here, except maybe a lack of research.

My mother's hearing is pretty bad now, and I had to talk a professional audiologist through tuning her aids for maximum intelligibility. I couldn't fault his personal skills, but the consonant/vowel heuristic he'd learned in training was oversimplified and not giving good results.

He'd basically set up a phone curve filter, but in fact you need some low-mid for good intelligibility, especially on male voices. Once he dialed that back in everyone was happy.

Thing is, we needed three one hour sessions to get it in the ballpark. The real problem with aids isn't the technology, it's the fact that setting up a good prescription is really difficult and time-consuming - even more so for elderly people who may have problems describing what they're hearing.

[raverbashing]

"Feedback comes from bad electronic/DSP design"

I see that you mention an adaptive filter, and that might be a good solution, however, you are limited by CPU power of the system and other constraints (like having to work continuously)

Bonus points if you tell me what are the poles and zeros of that system to avoid feedback.

[jimktrains2]

> other constraints (like having to work continuously)

I'd vote that next to no delay is a stronger constraint. With skype, you're already delayed, so adding a little processing isn't an issue. With a hearing aid, if there is too strong a delay it because off putting and, at times, dangerous.

But yeah, CPU and Power constraints in something about the size of the first joint of my pinky (including battery) are tight and very limiting.

[rplst8]

> Feedback comes from bad electronic/DSP design.

Absolutely wrong. Feedback comes from a loop gain of > 1. Period. Microphone and speaker proximity have everything to do with it.