SNR on different DSL types

I think I'm right if I say that the higher the SNR on fixed speed ADSL, the better the quality of the line is
What I was wondering is what a good SNR on Max or LLU would ideally be? I thought that if on Max or LLU and at 6db SNR with CRC / HEC errors less than a few an hour, on fastpath and stable your would likely have a very good line.
Most of the SNR's I've seen (probably about 95%) on LLU have been at 6db
I'm not so sure about Max though, but generally I think the SNR tends to be between 6db and 10db, e.g would an SNR of 7db on Max with an extremely low upstream and attenuation indicate a problem.
The reason I ask is that I was never on Max, so never really bothered getting to grips with Max stats too much and now I regualrly help users connecting to Be some estimate of their estimated speed, I sometimes get a bit lost

'Vanilla' ADSL gives you whatever SNR the fixed speed allows, whereas max is the other way about, and drives the speed as high as possible within a given SNR band.

On a fully rate adaptive DSL its a balance between noise margin , sync speed and errors.
You trade noise margin for a higher sync rate, but at the risk of a higher error rate and possible disconnection if the noise margin fluctutates.
Many providers will set a target noise margin of 6dB, meaning the DSLAM will try and obtain the highest line rate whilst maintaining a 6dB margin. Some(e.g. Tiscali) may set a higher target noise margin , presumably for stability and reduced support calls, but at the expense of a higher line rate.
Broadband Max is limited to upto 8Mbits line rate whereas some LLU can obtain upto 16,22 or 24mbits . Someone syncing at full rate on Broadband Max may still manage 10dB noise margin ,whilst another may `only' manage 2Mbits on a 6dB margin (6dB being the target, although this can be raised to improve stability).

The only real difference between MAX and LLU is the BT BRAS profile system. LLU and MAX will have the same performance on the same line assuming ADSL1, BRAS profile excepted, ADSL2+ will of course be generally better at the same SNR margin. The minimum acceptable target SNR will depend on the ISP, most use a minimum 6db target, but there are both MAX and LLU ones that specify a 9db minimum to increase stability, i.e support calls, at the cost of some speed.

The more margin you have above the minimum target SNR the more stable your line will be and the more resistant to noise bursts and yes, usually the higher the SNR on a fixed line then usually the better the line meaning the better the speed you are likely to get going to MAX/LLU.

As most ISPs use a target SNR margin of 6db for MAX then any margin in excess of that will be traded for speed. A 7db margin on a line with low attenuation that is probably maxing out the speed of the line is fine, though it might indicate a steady noise level not allowing a larger margin. If it is fairly steady state background noise that doesn't change much over time so that the actual 7db changes little then it is unlikely to be a problem though it wouldn't leave much headroom for large noise bursts.

weirdly On 2mb my SNR fluctuated from 26db to 0db at random intervals, even losing sync. Since moving to MAX on Friday (synced at 7776kbps) the SNR has remained 6-7db constantly.

Go figure!

What router are you using?