Simulcasting

Simulcast, a portmanteau of simultaneous broadcast, is the broadcasting of programs or events across more than one medium, or more than one service on the same medium, at exactly the same time. For example, Absolute Radio is simulcast on both AM and on satellite radio, and the BBC's Prom concerts were formerly 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. In the 1970s WPXI in Pittsburgh broadcast a live Boz Scaggs performance which had the audio simultaneously broadcast on two FM radio stations to create a quadrophonic sound, the first of its kind. The first such transmission was in 1975, 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).

Similarly, in the 1980s, before Multichannel Television Sound, or home theater was commonplace in American households, broadcasters would air a high fidelity version of a television program's audio portion over FM stereo simultaneous with the television broadcast. PBS stations were the most likely, especially when airing a live concert. It was also a way of allowing MTV and similar music channels to run stereo sound through the cable-TV network. This method required a stereo FM transmitter modulating MTV's stereo soundtrack through the cable-TV network and customers connecting their FM receiver's antenna input to the cable-TV outlet. Then they would tune the FM receiver to the specified frequency that would be published in documentation supplied by the cable-TV provider.

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