I found
http://whirlpool.net.au/forum-replies-archive.cfm/341026.html
It's a long post. seach "Jock M", He is the guy know ADSL. according to him,
Bad : 0-6
Fair : 6-10
Good : 10-15
Fair : 15-20
Bad : 20-30
Also check http://forums.whirlpool.net.au/index.cfm?a=wiki&tag=ADSL_Theory,
Although I can't really understand it, I tend to believe what it says.
"
At first glance if SNR is very high then it's good: almost no noise which drives the ratio higher. And the less noise the better and easier for modem.
Unfortunately some noise is always present and noise always has frequency distribution. Which means all spectrum is polluted by noise (strictly speaking different parts of it are polluted to different extent). So the less spectrum you use the less noise you are getting. ADSL is using spectrum in small chunks so if someone (SNR setting on DSLAM) is forcing you (the modem) to have very good SNR, then you might limit the spectrum you use in order to get rid of the noise.
"
http://whirlpool.net.au/forum-replies-archive.cfm/341026.html
It's a long post. seach "Jock M", He is the guy know ADSL. according to him,
Bad : 0-6
Fair : 6-10
Good : 10-15
Fair : 15-20
Bad : 20-30
Also check http://forums.whirlpool.net.au/index.cfm?a=wiki&tag=ADSL_Theory,
Although I can't really understand it, I tend to believe what it says.
"
At first glance if SNR is very high then it's good: almost no noise which drives the ratio higher. And the less noise the better and easier for modem.
Unfortunately some noise is always present and noise always has frequency distribution. Which means all spectrum is polluted by noise (strictly speaking different parts of it are polluted to different extent). So the less spectrum you use the less noise you are getting. ADSL is using spectrum in small chunks so if someone (SNR setting on DSLAM) is forcing you (the modem) to have very good SNR, then you might limit the spectrum you use in order to get rid of the noise.
"