[Asterisk-Users] Woodpeckers

[Chris Albertson]

Get a spectrum analizer.  

Software will do it.  Record the humming connetion to a file
and then run it through software that plots a power spectrum.
THere is plent of good open source software.  Even some audio
file ditors have this feature.  You should be able to see the
hum as periodic peaks at the multiles of 60hz.  You can't even
begin to talk about how to fix this without such a plot.

--- Greg Hill <gregh-asterisk at hillnet.us> wrote:
> On Fri, 20 Feb 2004, matt wrote:
> 
> > I would have thought that should have been gotten rid of...
> >
> > Notch filter would only get rid of the fundamental frequency unless
> you
> > notch at the harmonics also.
> >
> > Best bet I would say is a high pass filter at say 500hz.
> >
> > Reasonably simple to make with a resistor and capacitor... I think
> Sound
> > On Sound magazine (which has archives on the web) had an article on
> how
> > to build one...
> >
> > The thing is, most of the codecs available in * should be high and
> low
> > pass filtering it anyway...
> 
> My first thought was an RC filter, too. But I'd suggest that 500 Hz
> is too
> high a cutoff, because a note like a middle C is 256 Hz. I don't
> think
> it's uncommon for a voice (especially a male voice) to be in that
> range
> frequently. Although (in English, at least) vowels generally have a
> low
> frequency and sharp consonants (like a t) have a high frequency. It's
> the
> consonants which do the most for understanding a word, so maybe
> having
> those low frequencies attenuated wouldn't be so bad after all.
> 
> But as somebody else pointed out, a first-order RC filter probably
> wouldn't attenuate quickly enough. By the time you get into a
> multi-order
> filter, it's probably best to be doing it in software (since the
> signal is
> going to be digitized anyway).
> 
> Greg
> 
> 
> 
> 
> >
> > Matt
> >
> > Michael Welter wrote:
> >
> > > I live at 8000' in the Rockies.  We have lots of
> woodpeckers--they
> > > especially love to drill 4" holes in the north side of my house.
> > >
> > > They also like to drill on the arial telephone cables.  Water
> then
> > > gets into the cable and causes a partial grounding on the
> circuits.
> > > This causes 60Hz hum to be heard on the line as well as a loss of
> > > amplitude.  Qwest says tough s--t.
> > >
> > > All three of my POTS lines have hum.  They are connected to an
> Adtran
> > > 750 and my asterisk system (a testbench for commercial
> endeavors.)
> > >
> > > The hum has always been bad on my end.  Since I installed *,
> several
> > > of my callers have remarked about the hum.
> > >
> > > So here's the question:  Could a notch filter of sorts be
> installed in
> > > the codecs I use?  Filter-out everything between, say, 55 and
> 65Hz?
> > >
> > > Alternatively, is there a feature on the Adtran FXO card that
> deals
> > > with this?
> > >
> > > Thanks for your help,
> > > Mike
> > >
> > >
> > >
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=====
Chris Albertson
  Home:   310-376-1029  chrisalbertson90278 at yahoo.com
  Cell:   310-990-7550
  Office: 310-336-5189  Christopher.J.Albertson at aero.org
  KG6OMK

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