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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.

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. 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).

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.

The first ever concert "simulcast" was Frank Zappa's Halloween shows (October 31, 1981), live from NYC's Palladium and shown on MTV with the audio-only portion simulcast over the FM "Starfleet Radio" network. A later, notable application for simulcasting in this context was the Live Aid telethon concert that was broadcast around the world in July 13, 1985. Most destinations where this concert was broadcast had the concert simulcast by at least one TV network and at least one of the local FM stations.

Most stereo-capable video recorders made through the 1980s and early 1990s had a "simulcast" recording mode where they recorded video signals from the built-in TV tuner and audio signals from the VCR's audio line-in connectors. This was to allow one to connect a stereo FM tuner that is tuned to the simulcast frequency to the VCR's audio input in order to record the stereo sound of a TV program that would otherwise be recorded in mono. The function was primarily necessary with stereo VCRs that didn't have a stereo TV tuner or were operated in areas where stereo TV broadcasting wasn't in place. This was typically selected through the user setting the input selector to "Simulcast" or "Radio" mode or, in the case of some JVC units, the user setting another "audio input" switch from "TV" or "Tuner" to "Line".

Other uses

In America, simulcast most often refers to the practice of offering the same programming on an FM and AM station owned by the same entity, in order to cut costs. With the advent of solid state AM transmitters and computers, it has become very easy for AM stations to broadcast a different format without additional cost; therefore, simulcast between FM/AM combos is rarely heard today. Normally, AM stations broadcast some type of talk format; depending on the population, the format may be ethnic. During National Party rule in South Africa, many programs were dubbed in Afrikaans. The English soundtrack was available on Radio 2000. This could be selected using a button labeled simulcast on many televisions manufactured before 1995.

Radio programs have been simulcast on television since the invention thereof; however, as of recent, perhaps the most visible example of radio shows on television is The Howard Stern Show, which currently airs on SIRIUS Satellite Radio as well as Howard TV. Another prominent radio show that is simulcast on television is Imus in the Morning, which airs on RFD-TV in addition to Citadel Media.

In another case, popular programs will be aired simultaneously on different services in adjacent countries, such as The Simpsons, airing Sunday evenings at 8:00 p.m. (Eastern and Pacific times) on both Fox in the United States and Global in Canada. "Simulcast" is often a colloquial term for the related Canadian practice of simultaneous substitution (simsub).

In sports, simulcasts are when a single announcer broadcasts play-by-play coverage both over television and radio. The practice was common in the early years of television, but since the 1980s, most teams have used a separate team for television and for radio.

As all NFL television broadcasts are done by the national networks or via cable, there are no regular TV-to-radio football simulcasts. However, NFL rules require that games airing on cable and satellite networks (ESPN, NFL Network) are simulcast on local over-air TV stations in markets serving the two local teams participating in each game.

Similarly, no current National Basketball Association teams use a simulcast. Al McCoy (Phoenix), Chick Hearn (Los Angeles Lakers), Kevin Calabro (Seattle) and Rod Hundley (Utah) were the last NBA team broadcasters to simulcast.

In Major League Baseball, only Vin Scully continues the practice; however, he simulcasts only the first three innings of Los Angeles Dodgers games at Dodger Stadium and other National League Western Division parks.

The practice is most prevalent in the National Hockey League where three teams simulcast:

Simulcasts via satellite can be a challenge, as there is a significant delay because of the distance - nearly 50,000 miles (80,000 km) round-trip - involved. Anything involving video compression (and to some extent audio data compression) also has an additional significant delay, which is noticeable when watching local TV stations on direct broadcast satellites. Even though the process is not instantaneous, this is still considered a simulcast because it is not intentionally stored anywhere.

(Multiplexing -- also sometimes called "multicasting" -- is something of a reversal of this situation, where multiple program streams are combined into a single broadcast. The two terms are sometimes confused.)

In horse racing, a simulcast is a broadcast of a horse race which allows wagering at two or more sites; the simulcast often involves the transmission of wagering information to a central site, so that all bettors may bet in the same betting pool, as well as the broadcast of the race.

On cable television systems, analog-digital simulcasting (ADS) means that analog channels are duplicated as digital subchannels. Digital tuners are programmed to use the digital subchannel instead of the analog. This allows for smaller, cheaper cable boxes by eliminating the analog tuner and some analog circuitry. On DVRs, it eliminates the need for an MPEG encoder to convert the analog signal to digital for recording. The primary advantage is the elimination of interference, and as analog channels are dropped, the ability to put 10 or more SDTV (or two HDTV, or various other combinations) channels in its place. The primary drawback is the common problem of over-compression (quantity over quality) resulting in fuzzy pictures and pixelation.

In universities with multiple campuses, simulcasting may be used for a single teacher to teach class to students in two or more locations at the same time, using videoconferencing equipment.

In many public safety agencies, simulcast refers to the broadcasting of the same transmission on the same frequency from multiple towers either simultaneously, or offset by a fixed number of microseconds. This allows for a larger coverage area without the need for a large number of channels, resulting in increased spectral efficiency. This comes at the cost of overall poorer voice quality, as multiple sources increase Multipath significantly, resulting in what is called simulcast distortion.

With some of the latest Simulcast control equipment for FM radio networks, the distortion experienced is almost in-audible to the human ear. With the introduction of Line Equalisation Modules and Tone Generation Modules, the phasing advance and retard is so well calculated that the distortion is almost entirely averted.

The Tone Generation Module (or TGM) generates a pilot tone at 3300Hz which is then sampled by the Line Equalisation Module (or LEM) which each channel on each radio high site has 2 of located back at the main control site. This then determines the phase shift in the signal and adjusts the transmission accordingly such that all the overlap areas in transmission are in phase with each other.

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