Would you help me to undertand Volume Normalization and ReplayGain?

What's up...Taggers! (Read it like Davie504 would do it) :smile:

After cover songs another "problem" jumped on my mind: MP3 volume!
Now I read something about ReplayGain and Volume Normalization, but I would like to know more about it and what is the best way to deal with it.
From iTunes (I have OSX and hope Florian will give us an alpha version soon of the native application) I can see some files with negative numbers on the "Volume" tag, what does it mean? I don't know who put that values, maybe iTunes itself? Should I clear all the TAGs (which one?) and let some utility (iTunes, MP3Tag, etc) work on my library and calculate values? Why values are always negative?

Thank to everyone will spend some times trying to answer me. :hugs:

You could start here:

WOW!
That's a great starting point and half of the solution.
But I need to understand why should I choose AlbumRG or just TrackRG, if there are some setting I should be aware of that could introduce clipping, I didn't understand if analysis should happen to the whole library or if it is incremental, etc.

Some sort of "Volume Normalization WiKi" :sweat_smile: