The site will not share mp3 @ http://cdn.periphery.org/audio/07. Melodic Toad.mp3. Says it is not an audio file. Downloading and playing it works, and the MIME type is correct, so not sure what the problem is!
I actually found the solution to this myself. The problem for me was files with spaces. Huffduffer doesn't like this. If you manually convert the spaces to %20 then you should be good to go. Seems like it'd be an easy fix from the backend side as well ;)