How to keep my music and alarm files separate
Folder player does that for you.
I use the pro version for years now. (I'm a fan).
But the free version works just fine for this purpose.
Just select a home folder in the settings. 
I always select the directory above the Music folder, so I'm able to shuffle trough al the mp3's.

Hope this works out for you.

https://play.google.com/store/apps/details?id=com.folderplayer