To use this function you must create empty files first.
•Select the audio file on which you want to associate an empty file.
•Do a right click on it and choose the "Masterize as" function (or right click on the "Generate a master" 
icon). A window is displayed proposing a list of empty files (without audio files associated) available in the Browser.
•Choose the empty file on which you want to associate the sound file.
•Click on "OK".
The sound is associated to the file and the status of this audio file will be master.