I downloaded it, tried it, and like the clean design.
One suggestion I have is to make the sleep timer more granular. Just allow the user to choose a specific number of hours and minutes instead of a fixed list of 5 min, 10 min, 30 min, 1 hr, 10 hr. The current set is too limited for me to use for sleep (to drown out noises after going to bed).
Another suggestion is to add more sounds. There seem to be many rain sounds but only one fire related sound.