I will go out on a limb here and say that the GPL has nothing whatsoever to do with copyrights that apply to music. In the US at least, unless you perform music that is exclusively in the public domain, you pretty much need to pay your dues to ASCAP/BMI or explain the their lawyers why you don't need to.
And anyway, I don't see that the GPL on source code is so enforce-able in most cases. I always assume that any code I release under the GPL is pretty much public domain. To subscribe/unsubscribe, point your browser to: http://www.tullochgorm.com/lists.html
