An acetate disc is a type of phonograph record generally used from the 1930s to the late 1950s for recording and broadcast purposes and sees limited use as of 2009. Despite their name, "acetate" discs do not contain any acetate.
Acetates of 12", 10", 7" sizes
Presto 8N Acetate disc engraver (1950) used by the Canadian Broadcasting Corporation to record radio programs
Electrical transcriptions are special phonograph recordings made exclusively for radio broadcasting, which were widely used during the "Golden Age of Radio". They provided material—from station-identification jingles and commercials to full-length programs—for use by local stations, which were affiliates of one of the radio networks.
Electrical transcription disc of The War of the Worlds radio broadcast by Orson Welles with this "dubbed" copy created ten years after the original broadcast