I have seen on an overseas forum that the SNR should be over 10db - so mine is okay.
But the same forum suggested the noise level should be no more than 1db for each km the line takes back to the exchange.
Give I am about 3 to 4km from the exchange (depending on exactly which route the Chorus cable takes), my noise level is way over this at 16 to 33db.
Is this an issue? What readings do others have?