Background Audio Access Keys Criterion

In multimedia make certain the volume of background audio plays at least 20 decibels quieter than that of the main audio content.

For people who are hard of hearing you should keep the volume of background audio low enough so they can distinguish the foreground audio.
As a general rule to make audio content accessible you should leave a 20 decibel difference.
Points - All or nothing.
Criterion weighting of two.