[WARC] Nic Net Tonight!

[Leslie Hittner]

I think most, if anot all, integrate. The DSP is quite simple.
My fireplace fan virtually disappears when I switch them "on."
My brother executed a long "hummmmmmm" as evenly as he could. No
change. Car road noise disappears, but intermittant bumps do
not. They cannot work too effectively in "real time" because the
acoustic noise cannot be delayed. The response, therefore, would
have to be nearly instantaneous and the DSP simply is not fast
enough.

When I switch mine on, there is a noticeable delay - say 80
milliseconds or so before the DSP negates the fan noise. In the
car, I noticed it was far more effective against the road/wind
noise than it was with the high pitch vibration of the
moister-coated antennas (Mine do that in the fog.)

I think these things are being marketed primarily to alleviate
jet noise and to make it easier to hear the movies in airliners.
They are usually demonstrated in stores by simulating jet
airliner cabin noise. Mine came with a variety of plug
converters that would be needed to adapt them to the various arm
rest sockets in jetliners.

A simpler non-DSP circuit might respond fast enough to reduce
transient or time-variable noise sources, but might be less
efficient on wide spectrum sources that do not vary
significantly with time. Even such a simple phase inverter might
leave irritating residuals as it must first electronically
"recognise" the signal before it can respond with an inverted
duplicate with the right amplitude because a feedback loop is
required. That very short time might be perceived as "static."

-Les


----- Original Message ----- 
From: <jarvis at jarviscomputer.com>
To: "Winona Amateur Radio Club general discussion"
<warc at lists.w0ne.org>
Cc: "Winona Amateur Radio Club general discussion"
<warc at lists.w0ne.org>; <litvan at acegroup.cc>
Sent: Monday, December 31, 2007 07:15
Subject: Re: [WARC] Nic Net Tonight!


> Hello All,
>
> My testing was with a vacuum cleaner as a noise source and the
noise
> canceling was effective.
>
> In a large room the conversations are not like discrete
signals but mix
> into a din.  My guess is that the noise canceling head phones
would help
> in this situation.   Do they really integrate or do they
listen and react?
>
> Clare
>
>
> > What kind of "noise" do noise cancelling headphones
eliminate?
> > These devices integrate noise over time and eliminate the
noise
> > by producing out-of-phase counterparts and linearly adding
the
> > two waves. That means they are most effective on stable
noise
> > sources, such as jet engine noise in airliners, components
of
> > vehicle road noise, etc. They are less effective on short
> > duration pulse noise and sounds whose spectra vary with time
> > (like speech.)
> >
> > In addition to the electronic noise elimination, noise
canceling
> > headsets usually feature very effective acoustic isolation
from
> > outside noise sources. I suspect such isolation, rather than
the
> > electronic DSP systems, is most effective in communications
> > center environments.
> >
> > I admit, I haven't listened to every noise canceling headset
on
> > the market, but this has been my experience. I actually
decided
> > not to purchase a pair but then I just got one from my son
for
> > Christmas. My experience with that set so far bears out my
other
> > observations and I believe I will most often use the headset
> > when flying.
> >
> > I know that Clare has a set of noise canceling headphones
and
> > would be interested in his observations, since I was unable
to
> > be in the net tonight.
> >
> > -Les
> >
> > ----- Original Message -----
> > From: "Len Litvan" <Litvan at acegroup.cc>
> > To: "W0NE Listserv" <warc at lists.w0ne.org>
> > Sent: Sunday, December 30, 2007 21:32
> > Subject: [WARC] Nic Net Tonight!
> >
> >
> >> Hi folks,
> >>
> >> That was a good net tonight--very informative.
> >>
> >> I especially liked the info about noise-canceling
headphones.
> > I was
> >> about to buy a conventional headset (to replace the Radio
> > Shack and
> >> assortment of other earphones around) but was not
considering
> > noise
> >> canceling types.
> >>
> >> The comments about noise canceling at emergency sites was a
> > big factor
> >> in persuading me to go upscale and get a noise-canceling
set.
> > Thanks
> >> for helping me spend our money wisely!
> >>
> >> 73,
> >> Len KC0RSX
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> >>
> >
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