What parks allow you to openly play music (i.e. instruments)?

In order to play instruments within Fairmount Park, you must obtain a permit from the Fairmount Park Commission. This also goes for loud radios and DJ-ed parties.

I have found, though, that many times as long as the music in question isn't disturbing the peace there usually isn't a problem. Many of the parks feature drum circles and musical groupings without permits because it does not bother the neighbors surrounding the parks. However, I would suggest, to be on the safe side, to get a permit so there is a guarantee of no problems.