Volume

Each song can have it's own Volume such that, when the song is played, it automatically sets the volume. To show the Volume meta data, context-click on the sort column headers, then pick "Volume" from the list. Now you can see the volume associated with each song.

To have a song remember it's volume, edit the Volume for that song and set it to 1. Then, when the song is playing, any adjustment you make to the volume knob will also cause the song to remember that volume.

To have a song "forget" it's volume, and just use the current setting on the volume knob, edit it's Volume and set it to zero.