how to have two applications play sound simultaneously? I want the music to keep playing in the background while I practice Spanish on this DuoLingo app. 
The music player stops while the duolingo is trying to play sound as of now. Is this possbile?
As for my device, whenever I play duolingo and music at same time then the audio fades slightly with CM 12 built-in player

Now if you are OK with any third party application. Here is it what you need to do. 


Install Poweramp Music Player .
Go to its settings.
Then click on audio.
Select Audio Focus.
Uncheck Short Audio Focus Change.

(Click image to enlarge)