I never heard of replay gain. What is it? What does it do?
In a nutshell, ReplayGain takes average audio level information that’s saved in the metadata header of the audio file. The volume of the Fuze is then tweaked up/down between tracks, so that they will play at the same desired level.
Once your files are scanned (analyzed) using one of various applications, the level information is added to your music files. Media Monkey, for example, can auto-level your music, then transfer it to your Fuze.
Check the post about ReplayGain in the highlighted “stickies” at the top of the Fuze forum page.