Topic summary
Simulcasting

Extracted from the Wikipedia article Simulcast.
Simulcasting to provide stereo sound for TV broadcasts
Before stereo TV sound transmission was possible, simulcasting on TV and radio was a method of effectively transmitting "stereo" sound to music TV broadcasts. Typically, an FM frequency in the broadcast area for viewers to tune their stereo systems to would be displayed on the screen. The band Grateful Dead and their concert "Great Canadian Train Ride" in 1970 was the first TV broadcast of a live concert with FM simulcast. 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 in the United Kingdom was on 14 November 1972, when the BBC broadcast a live classical concert from the Royal Albert Hall on both BBC2 and Radio 3. The first pop/rock simulcast was almost two years later, a recording of Van Morrison's London Rainbow Concert simultaneously on BBC2 TV and Radio 2 (see It's Too Late to Stop Now) on 27 May 1974.