In every country of the developed world, except the United States and Australia, sound recordings enter the public domain 50 years after they are first released, so recordings from 1955, for example, are now in the public domain in Europe, even though copies of them are still illegal copyright violations in the United States. The vast majority of pre-1965 sound recordings are simply unavailable at any price in the United States legally.
Rather than being governed by federal copyright laws (which bring works into the public domain prior to 1923), they are governed by state law protections that are virtually eternal. The 1998 Sonny Bono Copyright Term Extension Act (one of the most vile pieces of intellectual property legislation ever enacted) keeps pre-1972 sound recordings out of the public domain until 2067, even though some date to as far back as the 1890s. Strong intellectual property laws are holding back the U.S. economy, not advancing it.