What does that mean?
It means that, you can change the play-back order of files regardless of whether they are on the same album or not!. So without depending where or in what album the files are you can easily change their playback order simply by drag-drop while they are playing.
Anyhow, Xnoise also supports other features such as ...
*. Easy album management.
*. Various playlist types support.
*. Not only audio, but anything that Gstreamer is capable of, Xnoise will play (including videos).
*. lastFM embedded.
*. MP3 tag editing, etc...
So how can I install it on Ubuntu using PPA...
Well, open your terminal and issue the below command,
sudo add-apt-repository ppa:shkn/xnoise
sudo apt-get update
sudo apt-get install xnoise xnoise-plugins-core