The higher above the line the more damage you are doing faster. Red lining means that you are causing damage to your audio device(s).
If any of the bars are surpassing the above line you are red lining, red lining is not good. The headphone app doesn't show this kind of information but your EQ sets a line and sounds are shown as bouncing bars below it that correspond to each frequency. For instance I DJ tech house, house, dubstep, and drum & bass primarily and I don't often turn frequencies above there baselines (zero). It is worth noting that most music is mastered in such a way that it was intended to be listened to. When you turn any one frequency up or down you are either adding or subtracting emphasis. The XM4's give you the option to tweak frequencies 400 (bass), 1K (mids), 2.5K (mids), 6.3K (highs), and 16K (highs).
20-300 are your lows/bass frequencies, 300-5K are your mids/vocal frequencies, and 5K-20K are your high notes. Hey! I'm actually a DJ so can give a good idea of what each frequency is.
