Volume leveling is just a fancy name for normalization. We have a process where the jukebox can analyze the mp3 files and append a little piece of data about the peak volume to the ID3 tag. Then, when you turn on volume leveling, it reads this and normalizes the volume accordingly. You can also apply it when you burn CDs or transfer the MP3s to a portable device.

I haven't really played with it too much myself.