Hey, glad to see this new forum.
I'd like to revive an old question I posted at the DBPro forum, just in case someone has something new to contribute.
This was it:
"set music volume" only accepts integers as volume. That represents a jump from 0 to 1 when fading in and out.
That could be said as that "1" is the minimum volume for a music, and that is not low enough to make a good fade effect (in or out).
So when fading (setting music volume), the music "abruptly" starts or ends. Well, not very abruptly, but it can be noticed.
Suggested solutions were:

to have modified the volume previously with an external application, but sometimes music must be turned off unexpectedly, so this wouldn't be a perfect solution.

to use 200 as maximum volume, so the 0-1 volume 'jump' would be halved... Perhaps the best workaround by now.
Here is the old post with code & media examples:
http://forum.thegamecreators.com/?m=forum_view&t=83698&b=1
Any comments are appreciated