Today the compact disc or CD turns 30. The disc has been declining in sales due to the convenience of digital music. NPR reports, this decline represents a long line of turn over for the industry, in roughly the same 30-year cycle. “Sam Brylawski, the former head of the recorded sound division at the Library of Congress, says, ‘If you look at the last 110-115 years, the major formats all have about 20 to 30 years of primacy.'” These formats include the phonograph, the 78, the LP, the cassette, and then finally the CD.