Lost recordings made just after World War II of Holocaust survivors singing songs have been rediscovered at the University of Akron. These recordings were part of a project by Dr. David Boder, a Latvian Jewish psychologist who had settled in the United States in the 1920s and quickly made a name for himself in academia and as a clinician. He became an American citizen in 1932, but he traveled regularly to Europe and kept in touch with his family until the war disrupted movement and communications.
In May of 1945, just days after the Allies accepted Germany’s unconditional surrender, Boder got the idea to interview displaced persons, Holocaust survivors, victims of the dislocations and horrors of World War II. His aim was first to get a record of victims’ experiences while it was all still painfully fresh.
Some of the recordings were lost, some they just didn't have a way to listen to anymore, but they are now all safely digitized. You can read more here