[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.