"I synced up the two available performances of Brian Wilson singing "Don't Worry Baby" live in 1981 with The Beach Boys. The two performances are from July 4th 1981 (Washington DC), and July 5th 1981 (Long Beach, CA). As you can hear, Brian Wilson's voice was completely gone at this point, never again to fully recover.
(Hint: turn balance to the right to hear the rare July 4th performance by itself)"
http://www.youtube.com/watch?v=rb4BVjXLnWE