[Elecraft] Auto Notch Revisited.

[Fred Jensen]

I have severe traumatic hearing loss from one night many years ago when 
I still thought I was bulletproof and immortal and I'm pretty deaf above 
about 1200 Hz.  The Dept of Veterans' Affairs gives me hearing aids, 
replacing them every 5 or so years [Thank you US Taxpayers, you change 
my life!].  They are quite amazing, mine are Phonak.

They will "notch out" the siren on a fire truck.  They don't take it all 
the way out [sort of unsafe not to hear it at all], they do it almost 
instantly over some threshold amplitude, and the "notch" follows the 
pitch of the siren.  I suspect they are doing what Jim, K9YC, suggested 
in another email on this thread.

They have 5 different automatic "programs" for differing circumstances. 
  One is for music which they somehow recognize after about 3-5 seconds. 
  They will also suppress the wind noise in my truck in about 3-5 
seconds. I think that suppression is just a roll-off of the very high 
frequencies.

I rarely use the manual notch on CW.  I'm not on SSB very much but when 
I am and in a non-contest environment, I have used the auto-notch and I 
don't discern any artifacts from the K3.  On some bands, I use the NB 
all the time on CW, it *does* knock down some repetitive components in 
the power line hash.  I don't notice any artifacts, but I can create 
them with very aggressive settings.  NR makes SSB signals sound a bit 
strange and I rarely use it.

Incidentally, my hearing aids seem to have Bluetooth because they "talk 
to each other," apparently negotiating when to change programs.  They do 
all of this on 1.4 V from batteries about the size of a 10-32 nut.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2014 Cal QSO Party 4-5 Oct 2014
- www.cqp.org

On 8/1/2014 2:48 AM, David Woolley wrote:
> Whilst summing the inverted NR output doesn't sound logically any
> different from applying a custom filter, the tactic used by hearing aids
> (at least Oticon ones) is actually to determine the frequency and phase
> of the presumed interfering signal (howl round in that case) and add in
> an inverted version.
>
> That does, have the disadvantage that if the tone is really external and
> than goes away, the cancelling tone remains for a while and you actually
> get an interfering signal as an artifact.  That would mean that it would
> not work well for modulated tones, e.g. morse signals, rather than pure
> carriers.