[Asterisk-Users] Woodpeckers

[Rich Adamson]

> >>>
> >>Notching may not be that effective, as it will not deal with the
> >>harmonics. The analogue to digital converter should already be
> >>filtering  below 300Hz, so you probably have quite a lot of hum if it
> >>    
> >>
> >
> >300Hz is pretty high to filter out... it's still well within the rage of
> >voices. To compare, 300Hz is about a diatonic concert D.
> >  
> >
> Can you read? ALL PHONE CALLS ARE FILTERED HARD BELOW 300Hz. THAT IS HOW 
> ALL TELEPHONY HAS WORKED SINCE THE TIME OF ALEXANDER GRAHAM BELL.

Sorry, not true. Might be true of most line cards in electronic offices, but
that has absolutely nothing at all to do with the cable pair or the phone.
The telephones do _not_ have filters in them, and if you care to plot the
response curve for any phone, you'll see there isn't much roll off either.
Certainly not to the extent that a "real" filter would create.

But, that's all pretty much beside the point anyway. As has been pointed
out, 60hz hum (and its harmonics) result from a tip-to-ground vs ring-to-
ground imbalance, and _that_ needs to be addressed.