First off, it depends what country you're in. I believe the 50 years rule for recordings is British (someone help me out here?) and record labels keep trying to extend it.
Here in the U.S., the default rule for anything (books, music, recordings, paintings, etc.) created after 1/1/1978 is life of the author plus 70 years. However, for "works made for hire" (which, according to record labels, most sound recordings are) the copyright term is 95 years from publication or 120 years from creation. However, there are so many permutations from the default that the Cornell University law school has created
this handy chart.
Also remember that there is a difference between the "recording" and the "music" (and lyrics) that is recorded.
As to whether Happy Birthday to You is still under copyright: the answer is that ASCAP keeps collecting royalties on it. I happen to believe that it is in the public domain. A scholarly article about this is
here but my more simple explanation is that (1) the differences between it and the public domain song "Good Morning to All" are so insubstantial such as to not warrant separate copyright protection and (2) the "copyrighted" version of the song contains an improper publication date in the copyright notice which would put it in the public domain automatically. See
here for background.
