Those are excellent discernable differences. Sometimes the voice on duolingo is not as discernable. I'll explore that site for other pronunciations. One of the most difficult for me is simply finding the best pronunciation of ''är''. I hear it so many different ways.
As a native English speaker (but not an expert), I'd say that the adjective "drunken" requires an object. In other words, you can say "what shall we do with the drunken sailor", but not "what shall we do with the sailor who is drunken".
In general, "drunken" isn't really used in modern English outside of set phrases like the song I quoted. Stick with "drunk" in all cases and you should be fine.