Washington -- New digital recordings of events in U.S. history and early radio shows are at risk of being lost much faster than older ones on tape and many are already gone, according to a study on sound released. Even recent history — such as recordings from 9/11 or the 2008 election — is at risk because digital sound files can be corrupted, and widely used CD-R discs only last three to five years before files start to fade, said study co-author Sam Brylawski.

"I think we're assuming that if it's on the Web it's going to be there forever," he said. "That's one of the biggest challenges."

The first comprehensive study of the preservation of sound recordings in the U.S., released by the Library of Congress, also found many historical recordings already have been lost or can't be accessed by the public. That includes most of radio's first decade from 1925 to 1935.

Shows by musicians Duke Ellington and Bing Crosby, as well as the earliest sports broadcasts, are already gone. There was little financial incentive for such broadcasters as CBS to save early sound files, Brylawski said.

Digital files are a blessing and a curse. Sounds can be easily recorded and transferred and the files require less and less space. But the problem, Brylawski said, is they must be constantly maintained and backed up by audio experts as technology changes. That requires active preservation, rather than simply placing files on a shelf, he said.

The study co-authored by Rob Bamberger was mandated by Congress in a 2000 preservation law.

Those old analog formats that remain are more physically stable and can survive much longer than contemporary digital recordings, the study warns. Still, the rapid change in technology to play back the recordings can make them obsolete.

Recordings saved by historical societies and family oral histories also are at risk, Brylawski said.

"Those audio cassettes are just time bombs," Brylawski said. "They're just not going to be playable."

The study recommends several solutions and its findings will be followed by a National Recording Preservation Plan being developed by the Library of Congress later this year.

New training and college degree programs for audio archivists are essential to improve preservation, the study found. Currently, no universities offer degrees in audio preservation, though several offer related courses.

The study also calls for legal reforms to enable more preservation. A hodgepodge of 20th century state anti-piracy laws has kept most sound files out of the public domain before U.S. copyright law was extended to sound recordings in 1972. The study found only 14 percent of commercially released recordings are available from rights holders.

Later this year, the library will debut a National Jukebox online after securing a license to stream sound recordings controlled by Sony Music Entertainment.

"The more copies of historical recordings are out there, the safer they are," Brylawski said.

The study also calls for changes in copyright law to help preservation. As it stands now, Brylawski said, copyright restrictions would make most audio preservation initiatives illegal, the authors wrote.

Dwindling resources also hamper preservation efforts at many smaller libraries and archives. The study calls for more coordination among preservationists to prioritize efforts and develop techniques that can be used by institutions with smaller budgets.