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# Long description

A line graph is shown with the X axis labelled tone number. It is marked from 0 to 408 in increments of 17. The Y axis is labelled S/N ratio per tone in decibels and is marked from minus 20 (bottom) to 70 (top) in increments of ten.

The upstream signal is shown to the left of the graph, in green, starting just after tone number zero, at 0 decibels. It rises rapidly to a peak of just over 50 decibels at about tone number 17. It then falls back to about 40 decibels just before tone number 34, then drops rapidly to 0 decibels.

The downstream signal is shown in red and starts at 0 decibels where the upstream signal ends. The downstream signal rises rapidly from 0 decibels over the space of about 10 tones, rising to over 50 decibels around tone number 42 and at around tone 50. It then fluctuates as it drops steadily downwards. At several points, it drops to 0 decibels and then rises again to slightly below its original position. The downward fluctuation continues until tone number 365.