Why don't people think before they answer? It makes for such long dumb threads.an you read? ALL PHONE CALLS ARE FILTERED HARD BELOW 300Hz. THAT IS HOW ALL TELEPHONY HAS WORKED SINCE THE TIME OF ALEXANDER GRAHAM BELL.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.
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.
What I said is accurate. If the line card in the exchange filters hard below 300Hz there is no content below 300Hz in the signal, regardless of what the phone itself does. The phone call *is* filtered hard below 300Hz. Therefore, further filtering below 300Hz at the CPE will not remove anything significant that was in the received signal.
Regards, Steve
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