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Simulcast from WikiPedia:

Simulcast is a portmanteau of "simultaneous broadcast", and refers to programs or events broadcast across more than one medium, or more than one service on the same medium, at the same time. For example, Absolute Radio is simulcast on both AM and on satellite radio, and the BBC's Prom concerts are often simulcast on both BBC Radio 3 and BBC Television. Another application is the transmission of the original-language soundtrack of movies or TV series over local or Internet radio, with the television broadcast having been dubbed into a local language.

Before stereo TV sound transmission was possible, simulcasting on TV and Radio was a method of effectively transmitting "stereo" sound to music TV broadcasts. The first such transmission was in 1974, when the BBC broadcast a recording of Van Morrison's London Rainbow Concert simultaneously on BBC2 TV and Radio 2 (see It's Too Late To Stop Now).

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