The properties for the layout of background pictures for Audio Titlesets ('Audio only' titles) can be preset here.
IMHO it is easier to create a layout in the Audio Titlesets dialog and use the 'Set default' button there, as you have a preview function in this dialog. But to save the settings permanently in the registry, you need to use the 'Save' button here in the Default Settings dialog.
Enable or disable blurring for audiotitlesets and set up the values for X (horizontal) direction and Y (vertical) direction
See also: Using Blur
Default Type for Audiotitlesets: For dvdauthor you can select to create the audiofiles in a audiotitleset as either own titles or chapters. Using 'Titles', the timecode is reset after each audiofile. Using 'Chapters' the audiofiles are connected and the audiotitleset has a continuous timecode (you can nevertheless access each title individually from a menu). As in the official standard only 99 titles are allowed for a DVD (although many players have no problems with more than 100), I would recommend to use 'Chapters'. For MuxMan only the 'Chapters' mode is implemented.