When you level the track.. it uses the replay gain values to alter the actual volume of the track.
If you don't level the tracks, it uses the replay gain values to normalize the tracks while playing them if you have level playback volume turned on.
Does that help make sense of it?
In regard to the comments regarding track vs album gain.
I am a STRONG believer in customization and allowing users to choose according to their needs.
However, I'm also a big believer in protecting the users from making decisions that aren't necessarily in their best interest.
Don't crucify me, but I think that the way leveling is applied (using album gain), is the best option - even to the point of foregoing choice.
In a large part, this is because it cannot be undone very easily.
Consider this. If you change the level of the whole album using album gain, it roughly fixes most volume levels - though there will obviously be certain songs that are extremes... but it does do a rough job of it.
If you want to listen to an album, you can, and all the volumes will all be in sync with each other. If you want to listen to individual tracks, you can, and if the leveling is bad for you, you can run Mediamonkey's "level playback volume" feature which can use the track gain values - hence, you would get the exact same result as if you actually leveled it by track.
Of course, if playing on an ipod or other device you can sync with the appropriate settings to transfer the desires gain values across.
On the flipside however, consider this. If you change the level of each individual track to be normalized only relative to itself, you can listen to individual tracks at the your desired volume and you don't have to turn on "level playback volume" at all. However, if you EVER want to listen to an album, you can never get the tracks to sync volumes again and there is no magic "level back to album volume" setting in mediamonkey to do it for you. You are stuck with track volume forever.
So, even if it becomes an option in the future. I would suggest you use the "album" gain values to level your albums as it has the best of both worlds, where as using the "track" gain locks you into that, destroys the relationship between the songs on the album and is irreversible.. for no real advantage.
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