How do I equalize sound levels?

[Steven Vollom]

>Sometimes audio players will have plugins that
> "normalize" the levels of the audio they play, but I don't believe there's
> one that works system-wide.

Thanks Constantinos, I have wondered about that for a long time.  One short 
video file that I play just blasts when I turn it on.  There are others that 
require adjustment, but that one almost makes you crack a tooth.

Steven