Editor's Note: First Notes is a weekly update of recent happenings in the world of music.

* Outkast performed three sold-out nights in Atlanta to close out the band's 20th anniversary tour. Featuring plenty of guest appearances — including B.o.B., 2 Chainz, Future and Bigg Gipp - an estimated 20,000 people crammed into Centennial Olympic Park to watch the hip-hop duo go out with a bang. As for what the future holds, no one really knows.

* Black Sabbath has announced that it will record one more album before heading out on a final tour. The band released 13 last year, but singer Ozzy Osbourne said he'll do one more before he's 70.

* AC/DC's Malcolm Young is leaving the band after a variety of reports state the guitarist is suffering from dementia. A source close to the family stated the 61-year-old musician has a "complete loss of short-term memory." The band is set to release a new album, Rock or Bust, on Dec. 2.