Since Edison first captured sound from the air, and preserved it on strips of tin foil, people have stored sound as grooves cut into wax cylinders; as a pattern of magnetism on wire, or tape; even as flickering shades of grey, on movie film. Those grooves and bands of magnetism last for decades, perhaps even centuries. But the machines that bring the sound back to life fall apart much sooner. Think of that 8-Track tape player in your attic. And that turns those wires and tape into "dead media"; the sound is trapped, perhaps never to be heard again.
On this piece of Lost and Found Sound™, we resurrect sound from Dead Media, when we can. We hear a marine singing on the deck of a troop transport, during World War II, and Oscar Hammerstein recording his thoughts on a dictabelt.