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http://www.atlasobscura.com/articles/how-live-is-live-tv

....... " The history of intentional broadcast delay, or what is more commonly known today as the “seven-second delay,” actually has its roots in the days of radio. A primitive method of broadcast delay was first implemented by radio stations that would send out their signals down a telephone wire to a receiver in a different city hundreds of miles away, that would then return the signal, providing only milliseconds of delay thanks to the journey. Given the tiny amounts of time such a trick created, this method was not used for censorship or control so much as to increase sound clarity and depth when it was layered over itself.

It was not until the introduction of magnetic tape that live delay as we know it came about, although it was still all about physical distance. The earliest invention of intentional delay as we understand it seems to date back to Pennsylvania radio station WKAP in 1952. The system was initially developed to allow “live” on-air broadcasts of listener phone calls. Up until that point, only one side of a phone conversation could be aired due to FCC privacy regulations. In order to create what we now know as the common radio call-in format, the engineers at the station set up a system in which the broadcast would be recorded to one reel and broadcast off another, just seconds later—skirting the regulations but making it so that the calls weren’t truly “live.” Once again, the delay time between when the show was recorded and broadcast was determined by how long it took for the recording to get from one reel to the next—in other words, the physical length of the path between......"

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