So I’ve got some reverb going on with my hearing aids. Mostly when listening to music over the radio. Some with background noise. My audiologist said something about this can happen when there’s a delay between the hearing aid producing the sound and it reaching my ears naturally. No idea, but…
I don’t know if reverb is the right word. It’s not like an echo, but more like a vibration.
Anyone experience this? Is it a bad fit with my domes so sound it going around them? Any ideas?
I would think that sound going around the aids would cause feedback.
Is you audi a true audiologist or just a hearing aid sales and fitter. I ask that because that just does not seem to be valid.
But I don’t really know, and any odd sound or feeling I have ever had the audiologist has been able to adjust out and give me a comfortable sound feel. I have been wearing aid now for 40 years.
I have never worn domes as my audi told me they were not suitable for my hearing loss.
Just to be clear: you’re not streaming to the radio from your aids? Cuz that would involve a whole 'nuther level of technology and possible connectivity issues.
YEARS ago, I also had vibration from my radio, from shifting my car (yes, even a manual transmission triggered it), and occasionally even speech in large classrooms. I think I had a faulty diaphragm in the aids? It was 30 years ago tho …
Anyway, have your audiologist/dispenser actually check the aids for any kind of faulty part: hardware or software issue. No way should a new pair of aids deliver vibration with sound the way you describe. It sounds like a frequency-handling issue to me - but I’m NO expert.
So the battery died in my left hearing aid today and guess what… This reverb, vibration, echo… whatever it was stopped happening. Is it possible that one hearing needs to be adjusted and is ‘out of sync’ with the other one? Like a milisecond slower or something?
Despite what is said above about your hearing specialist, canal reverb is a thing that occurs when the directly incoming sound (usually around 1khz) is out of phase with the amplified sound. You get some weird artefacts from it.
There’s a feature in Sonova product( and possibly others) to smooth this issue, but changing the venting and tweaking the higher input level gain down around 1khz will usually yield some improvement.
Curious if the two aids are programmed the same or not. Processing can add lag to the sound and if you are combining that with live sound direct to the ear (like through the vents) then you can get some distortion for lack of a better term. This would be perceived as phasing or flanging if mild, reverb/echo/delay if more severe. You can learn about what each sounds like on Youtube.
If you are on the cusp of feedback you can hear kind of a metallic, tubular effect. I forget what the effect is called.
Um_bongo, thank you for your explanation. I think I’ve experienced this effect. But I can’t understand what situations would result in the incoming sound being out of phase with the amplified sound. It seems to me that all sounds reach my ear and hearing aid at the same time, and the only delay would be associated with the hearing aid amplification, which I understand to be quite fast in modern hearing aids.
If you’re aware of amplifier design there’s the opportunity for each stage to invert the signal, but that shouldn’t be the case - unless there’s an indavertent op-amp stage. However, hearing aids do have a processing delay of X usec (1/1000 seconds), so for the relevant frequencies when sound travels at 330m/s your amplified wave is going to be out of phase by 180 degrees with the incoming signal due to the phase delay induced vs the unamplified signal. The primary/lowest harmonic for the first 180 shift will always be the worst point for this as the waves are wider so there will potentially be more overlap.
Various things are done with the sound to mitigate against this effect, Phonak notably shifts the frequencies a degree to stop the peaks being congruent. Other manufacturers take different approaches. The problem with tacking it is that you can introduce interference/warbling as the peaks align and then deviate. Though their more recent aids have included a damping system to keep this in check.
The best thing you can do as a user is to either accept a degree more occlusion or speak to your audiologist and take in a sample of the sounds that cause it on your phone. Get them to wind down the gain a little in the area where the aid becomes unstable - especially for louder input levels.
Um_bongo, thanks again for your explanation. I think I understand most of it. Perhaps this is a nit, but if your u in usec is a Greek mu, shouldn’t that be 1/1000000 seconds. I had presumed that HA processing delay was more like microseconds than milliseconds. Also a question: is this delay approximately inversely proportional to the processor speed? Or does this depend more on the specific circuit and algorithm design? If it’s just processor speed, that’s increasing steadily, so shouldn’t this problem go away in a decade or so/
Micro here means, 1/1000, which is Mu. 1/1000000 is Pico.
The problem won’t go away with faster processing it just moves where the resonance is likely to hit, instant processing isn’t a thing yet, cause you can’t sample/process in real time.