Broadcasting over FM frequencies of two sound signals within a single channel. A multiplexing technique is utilized.
"In 1950 my grandfather gave an Armistice Day speech that was broadcast over a local radio station. That station provided him with a 16” transcription of that speech. Due to its fragility and the warning that it would deteriorate significantly after just a few playings, to my knowledge it was never played. I checked locally and there was no ..."