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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 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.
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. In the 1970s WPXI in Pittsburgh broadcast a live Bos Scaggz 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.
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 on 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".
In the mid to late 1990s, video game developer Nintendo utilized simulcasting to provide enhanced orchestral scoring and voice-acting for the first ever "integrated radio-games" – its Satellaview video games. Whereas digital game data was broadcast to the Satellaview unit to provide the basic game and game sounds, Nintendo's partner, satellite radio company St.GIGA, simultaneously broadcast the musical and vocal portion of the game via radio. These two streams were combined at the Satellaview to provide a unified audiotrack analogous to stereo.
The term "simulcast" (describing simultaneous radio/television broadcast) was coined in 1948 by a press agent at WCAU-TV, Philadelphia. NBC and CBS had begun broadcasting a few programs both to their established nationwide radio audience and to the much smaller--though steadily-growing--television audience. NBC's "Voice of Firestone" was an early example. Toscanini's NBC Symphony performance of 15 March 1952 is perhaps a first instance of radio/TV simulcasting of a concert, predating the much-heralded rock concert simulcasts beginning in the 1980s.
Presently, in the United States, 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 combinations are 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 foreign programmes on SABC television were dubbed in Afrikaans. The original soundtrack, usually in English, but sometimes in German or Dutch was available on the Radio 2000 service. 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 wrestling the first simulcast happened on March 26, 2001 between WWF Raw is War and WCW Monday Nitro.
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).
Simulcasting of sporting events
In sports, such as American football and baseball, 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) be 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), 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 more prevalent in the National Hockey League where two teams currently simulcast:
- The Buffalo Sabres with Rick Jeanneret and Rob Ray
- The Dallas Stars with Ralph Strangis and Daryl Reaugh (popularly known as "Ralph and Razor")
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 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 interference 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 3300 Hz 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.
Simulcasting of anime
In the anime industry, simulcast has come to mean anime TV shows that are streamed online with English subtitles for viewers outside of Japan within approximately 24 hours of the original Japanese broadcast. The term has also sometimes been used to mean shows streamed in this way several days after the original broadcast. Anime simulcasts are made possible by agreements between Japanese anime studios and American companies such as CrunchyRoll, FUNimation, Viz Media, or Hulu. 
- (Japanese) Nintendo. BS-X: Sore wa Namae o Nusumareta Machi no Monogatari (in Japanese). (Nintendo/St.GIGA). Satellaview, (v1995/8/8). (February 13, 1995) Kabe shinbunsha: ８月６日（日）、世界初のジオ／ゲー動プログラム「ＢＳゼルダの伝説」が大好評につき９月の再放送がついに決定した。
- "Satellaview: juegos desde el espacio." Atomicx. pp.54-57. July 2009.
- John Crosby, "Television Headache in Etymology," Oakland (CA) Tribune, 15 June 1948.
- "Simulcast - Anime News Network". Anime News Network. Retrieved 2013-02-19.
- Landa, Amanda (2010-07-02). "Niche Market, Global Scale: Simulcasting Anime Online". Retrieved 2013-02-19.
- Aeschliman, Lesley. "What Is Simulcasting? - Anime". Retrieved 2013-02-19.