Line attenuation is in relation to the “loop loss” on your line. The lower this figure the better, and the better chance you have of getting the faster speeds.
Attenuation is a term used to describe the reduction of the adsl signal strength that occurs on the copper pair over distance and is measured in dB decibels.
SNR is Signal to Noise Ratio – in other words a measurement in decibels of the Signal strength to the level of Noise on the line.
The higher your SNR is, the better, as there is less background Noise.