[Asterisk-Users] Woodpeckers

[Greg Hill]

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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