Multichannel Television Sound, better known as MTS, is the method of encoding three additional
audio channel
An audio signal is a representation of sound, typically using either a changing level of electrical voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric poten ...
s into an
analog
Analog or analogue may refer to:
Computing and electronics
* Analog signal, in which information is encoded in a continuous variable
** Analog device, an apparatus that operates on analog signals
*** Analog electronics, circuits which use analog ...
NTSC
The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...
-format
audio
Audio most commonly refers to sound, as it is transmitted in signal form. It may also refer to:
Sound
*Audio signal, an electrical representation of sound
*Audio frequency, a frequency in the audio spectrum
*Digital audio, representation of sound ...
carrier. It was developed by the Broadcast Television Systems Committee, an industry group, and sometimes known as BTSC as a result.
MTS worked by adding additional audio signals in otherwise empty portions of the television signal. MTS allowed up to a total of four audio channels. Normally two were broadcast to produce the left and right stereo channels. An additional
second audio program
Second audio program (SAP), also known as secondary audio programming, is an auxiliary audio channel for analog television that can be broadcast or transmitted both over-the-air and by cable television. Used mostly for audio description or oth ...
(SAP), could be used to broadcast other languages or entirely different audio like weather alerts that could be accessed by the user, typically through a button on their
remote control
In electronics, a remote control (also known as a remote or clicker) is an electronic device used to operate another device from a distance, usually wirelessly. In consumer electronics, a remote control can be used to operate devices such as ...
. The fourth channel, ''PRO'', was only used by the broadcasters.
History
Initial work on design and testing of a stereophonic audio system began in 1975 when Telesonics approached
Chicago
(''City in a Garden''); I Will
, image_map =
, map_caption = Interactive Map of Chicago
, coordinates =
, coordinates_footnotes =
, subdivision_type = Country
, subdivision_name ...
public television station
WTTW
WTTW (channel 11) is a PBS member television station in Chicago, Illinois, United States. Owned by not-for-profit broadcaster Window to the World Communications, Inc., it is sister to commercial classical music radio station WFMT (98.7 FM). The ...
. WTTW was producing a music show titled ''
Soundstage
A sound stage (also written soundstage) is a soundproof, large structure, building, or room with large doors and high ceilings, used for the production of theatrical film-making and television productions, usually located on a secured movie or ...
'' at that time, and was
simulcast
Simulcast (a portmanteau of simultaneous broadcast) is the broadcasting of programmes/programs or events across more than one resolution, bitrate or medium, or more than one service on the same medium, at exactly the same time (that is, simultane ...
ing the stereo audio mix on local
FM stations. Telesonics offered a way to send the same stereo audio over the existing television signals, thereby removing the need for the FM simulcast.
Telesonics and WTTW formed a working relationship and began developing the system which was similar to FM stereo modulation. Twelve WTTW studio and transmitter engineers added the needed broadcast experience to the relationship. The Telesonics system was tested and refined using the WTTW transmitter facilities on the
Sears Tower
The Willis Tower (originally the Sears Tower) is a 108- story, skyscraper in the Loop community area of Chicago in Illinois, United States. Designed by architect Bruce Graham and engineer Fazlur Rahman Khan of Skidmore, Owings & Merrill (SOM ...
.
In 1979, WTTW had installed a stereo
Grass Valley
A grass valley (also vega and valle) is a meadow located within a forested and relatively small drainage basin such as a headwater. Grass valleys are common in North America, where they are created and maintained principally by the work of b ...
master control switcher and had added a second audio channel to the
microwave
Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ran ...
STL (Studio Transmitter Link). By that time, WTTW engineers had further developed stereo audio on
videotape recorder
A video tape recorder (VTR) is a tape recorder designed to record and playback video and audio signal, audio material from magnetic tape. The early VTRs were reel-to-reel, open-reel devices that record on individual reels of 2-inch-wide (5.08& ...
s in their plant, using split audio track heads manufactured to their specifications, outboard record electronics, and
Dolby noise reduction
A Dolby noise-reduction system, or Dolby NR, is one of a series of noise reduction systems developed by Dolby Laboratories for use in analog audio tape recording. The first was '' Dolby A'', a professional broadband noise reduction ...
that allowed ''Soundstage'' to be recorded and electronically edited. In addition, an
Ampex
Ampex is an American electronics company founded in 1944 by Alexander M. Poniatoff as a spin-off of Dalmo-Victor. The name AMPEX is a portmanteau, created by its founder, which stands for Alexander M. Poniatoff Excellence.AbramsoThe History ...
MM1100, 24-track audio recorder was also used for music production and mixing.
PBS
The Public Broadcasting Service (PBS) is an American public broadcasting, public broadcaster and Non-commercial activity, non-commercial, Terrestrial television, free-to-air television network based in Arlington, Virginia. PBS is a publicly fu ...
member stations who wished to deliver ''Soundstage'' in stereo were provided with a four-track (left, right, vertical drive, and
time code
A timecode (alternatively, time code) is a sequence of numeric codes generated at regular intervals by a timing synchronization system. Timecode is used in video production, show control and other applications which require temporal coordinatio ...
) audiotape that could be synced with the video machines in those cities.
During the FCC approval process, several manufacturers applied to the FCC for consideration. Most notably the
Electronic Industries Alliance
The Electronic Industries Alliance (EIA; until 1997 Electronic Industries Association) was an American standards and trade organization composed as an alliance of trade associations for electronics manufacturers in the United States. They devel ...
(EIA) and Japanese EIA asked to be included in order to represent their members in the testing and specification phases of the approval process. WTTW engineers helped set standards for
frequency response
In signal processing and electronics, the frequency response of a system is the quantitative measure of the magnitude and phase of the output as a function of input frequency. The frequency response is widely used in the design and analysis of sy ...
, separation, and other uses of the spectrum. They also provided program source material used for the testing and maintained the broadcast chain. A
3M 24-track audio recorder was used to allow the selection of 12 different stereo programs for testing. The
Matsushita Quasar TV manufacturing plant and laboratory, just west of Chicago, was used as the source for all testing of the competing systems. Following the testing, several questions were raised about the validity of some of the tests, and a second round of testing began.
WTTW installed a Broadcast Electronics prototype stereo modulator in October 1983 and began full-time broadcasting in stereo at that time using the Telesonics system prior to
Federal Communications Commission
The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdiction ...
(FCC) rule-making on the BTSC system. MTS was officially adopted by the FCC on 23 April 1984. Following EIA and FCC recommendations, the BE modulator was modified to meet BTSC specifications, and by August 1984 was in full-time use on WTTW.
Sporadic network transmission of stereo audio began on NBC on July 26, 1984, with ''
The Tonight Show Starring Johnny Carson
''The Tonight Show Starring Johnny Carson'' was an American late-night talk show hosted by Johnny Carson on NBC, the third iteration of the ''Tonight Show'' franchise. The show debuted on October 1, 1962, and aired its final episode on May 22, ...
'', although at the time only the network's New York City flagship station,
WNBC
WNBC (channel 4) is a television station in New York City, serving as the flagship of the NBC network. It is owned and operated by the network's NBC Owned Television Stations division alongside Linden, New Jersey–licensed Telemundo station WN ...
, had stereo broadcast capability; regular stereo transmission of NBC programs began during early 1985. ABC and CBS followed suit in 1986 and 1987, respectively.
FOX
Foxes are small to medium-sized, omnivorous mammals belonging to several genera of the family Canidae. They have a flattened skull, upright, triangular ears, a pointed, slightly upturned snout, and a long bushy tail (or ''brush'').
Twelve sp ...
was the last network to join in 1987, with the four networks having their entire prime-time schedules in stereo by late 1994 (
The WB
The WB Television Network (for Warner Bros., or the "Frog Network", for its former mascot, Michigan J. Frog) was an American television network launched on broadcast television on January 11, 1995, as a joint venture between the Warner Bros. ...
and
UPN
The United Paramount Network (UPN) was an American broadcast television network that launched on January 16, 1995. It was originally owned by Chris-Craft Industries' United Television. Viacom (through its Paramount Television unit, which pr ...
launched the following season with their entire line-ups in stereo). One of the first television receiving systems to include BTSC capability was the
RCA Dimensia
''Dimensia'' was RCA's brand name for their high-end models of television systems and their components ( Tuner, VCR, CD Player, etc.) produced from 1984 to 1989, with variations continuing into the early 1990s, superseded by the ProScan model li ...
, released in 1984.
From 1985 to 2000, the networks would display the disclaimer "in stereo (where available)" at the beginning of stereo programming, sometimes using marketing tags such as CBS's "StereoSound" to describe their institution of stereo service. Networks in Canada and Mexico, which also used the NTSC video standard, utilized MTS sound when made available.
DTV transition in the United States
As a component of the NTSC standard, MTS is no longer being used in U.S. full-power television broadcasting after the June 12, 2009
DTV transition in the United States. It remains in use in
LPTV
Low-power broadcasting is broadcasting by a broadcast station at a low transmitter power output to a smaller service area than "full power" stations within the same region. It is often distinguished from "micropower broadcasting" (more commonly ...
and in analogue
cable television
Cable television is a system of delivering television programming to consumers via radio frequency (RF) signals transmitted through coaxial cables, or in more recent systems, light pulses through fibre-optic cables. This contrasts with broa ...
. All
coupon-eligible converter box
A coupon-eligible converter box (CECB) was a digital television adapter that met eligibility specifications for subsidy "coupons" from the United States government. The subsidy program was enacted to provide terrestrial television viewers with ...
es (CECBs) are required to output
stereo sound via
RCA connector
The RCA connector is a type of electrical connector commonly used to carry audio and video signals. The name ''RCA'' derives from the company Radio Corporation of America, which introduced the design in the 1930s. The connectors male plug and ...
s, but MTS is merely optional for the
RF modulator
An RF modulator (or radio frequency modulator) is an electronic device whose input is a baseband signal which is used to modulate a radio frequency source.
RF modulators are used to convert signals from devices such as media players, VCRs a ...
that every CECB contains. NTIA has stated that MTS was made optional for cost reasons; this may have been due to a belief that MTS still required royalty payments to THAT Corporation, which is no longer true except for some digital implementations.
[Letter to NTIA, August 21, 2007 (THAT Corporation)](_blank)
/ref>
THAT has created consumer pages on the DTV transition and how it affects MTS. The site describes the situation by stating that most consumers with CECBs will end up with monaural
Monaural or monophonic sound reproduction (often shortened to mono) is sound intended to be heard as if it were emanating from one position. This contrasts with stereophonic sound or ''stereo'', which uses two separate audio channels to reproduc ...
TV sound, since RF-only connections are common and MTS is optional (and rare) for CECBs.
Specification
The original North American television standards provided a significant amount of bandwidth
Bandwidth commonly refers to:
* Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range
* Bandwidth (computing), the rate of data transfer, bit rate or thr ...
for the audio signal, 0.5 MHz, although the audio signal itself was defined to extend from 50 Hz to 15,000 Hz. This was centered on the audio carrier signal
In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform (usually sinusoidal) that is modulated (modified) with an information-bearing signal for the purpose of conveying information. This carrier wave usually has a ...
4.5 MHz above the video signal, and given 25 kHz on either side of the carrier, using only 15 kHz of it.
This meant the lower and upper 0.2475 MHz of the audio channel was unused. Due to the nature of the NTSC
The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...
color signals added in the 1950s, the upper parts of the color signal pushed into the lower audio sideband
In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, that are the result of the modulation process. The sidebands carry the information transmitted by the radio signal. The sidebands co ...
. With the audio signal centered within the 0.5 MHz channel, and the lower 0.25 MHz being partially infringed on by leftover video signal, the upper 0.25 MHz was left largely empty.[
MTS worked by adding new signals to the free portion of this upper 0.25 MHz allocation. The original audio signal was left alone and broadcast as it always had been. Under MTS, this is the Main Channel. The actual signal in this channel is constructed by adding together the two stereo channels to produce a signal largely identical to the original monoaural signals and can be received on any NTSC television even without stereo circuitry.][
A second channel is then added, the Stereo Subchannel, centered at 31.468 kHz and extending 15 kHz on either side. This left a small gap between the Main and Stereo signals, known as the Pilot, at the 15.734 kHz. This signal is also known as "H", or "1H", and its frequency is selected to be a harmonic of the video's horizontal scan signal so that it can be accurately recreated from the video signal using a ]phase locked loop
A phase-locked loop or phase lock loop (PLL) is a control system that generates an output signal whose phase is related to the phase of an input signal. There are several different types; the simplest is an electronic circuit consisting of a ...
. If there is any signal present at the 1H frequency, the television knows a stereo version of the signal is present.[
The Stereo Subchannel consisted of the same two audio signals, L and R, but mixed out of phase to produce the "L–R" signal, or "difference". This signal is sent at a higher amplitude and encoded using dbx compression to reduce high-frequency noise. To lower total average power, the carrier is not sent (which means there is no always-on signal at that frequency). On reception, the receiver uses the video signal to create the Pilot, and then examines that frequency to see if there is any signal present. If there is, the difference signal is extracted by filtering out the signal between 1H and 3H into a separate channel, and the carrier is re-created by adding 2H to this. This signal is then decompressed from its dbx format, and then fed, along with the original Main, to a stereo decoder.][ FM stereo radio works in the same fashion, differing mainly in that the equivalent to the H signal is 19 kHz, not 15.734.
SAP, if present, is centered on 5H, but encodes a monaural signal at lower audio fidelity and amplitude.][ The PRO signal is likewise encoded at 7H. A signal using all four channels extends only to about half of the available bandwidth in the original audio upper sideband.
]
Usage of audio channels
The second audio program
Second audio program (SAP), also known as secondary audio programming, is an auxiliary audio channel for analog television that can be broadcast or transmitted both over-the-air and by cable television. Used mostly for audio description or oth ...
(SAP) also is part of the standard, providing another language
Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by which humans communicate, and may be conveyed through a variety of met ...
, a video description
Audio description, also referred to as a video description, described video, or more precisely called a visual description, is a form of narration used to provide information surrounding key visual elements in a media work (such as a film or tele ...
service like DVS, or a completely separate service like a campus radio
Campus radio (also known as college radio, university radio or student radio) is a type of radio station that is run by the students of a college, university or other educational institution. Programming may be exclusively created or produce ...
station or weatheradio A weather radio is a specialized radio receiver that is designed to receive a public broadcast service, typically from government-owned radio stations, dedicated to broadcasting weather forecasts and reports on a continual basis, with the routine w ...
. This sub-carrier is at 5x horizontal sync and is also dBx encoded.
A third PRO (professional) channel is provided for internal use by the station, and may handle audio or data. The PRO channel is normally used with electronic news gathering
Electronic news-gathering (ENG) or electronic journalism (EJ) is usage of electronics, electronic video and sound recording and reproduction, audio technologies by journalist, reporters to gather and present news instead of using film camera ...
during news
News is information about current events. This may be provided through many different Media (communication), media: word of mouth, printing, Mail, postal systems, broadcasting, Telecommunications, electronic communication, or through the tes ...
broadcast
Broadcasting is the distribution of audio or video content to a dispersed audience via any electronic mass communications medium, but typically one using the electromagnetic spectrum ( radio waves), in a one-to-many model. Broadcasting began ...
s to talk to the remote location (such as a reporter
A journalist is an individual that collects/gathers information in form of text, audio, or pictures, processes them into a news-worthy form, and disseminates it to the public. The act or process mainly done by the journalist is called journalism ...
on-location), which can then talk back through the remote link to the TV station
A television station is a set of equipment managed by a business, organisation or other entity, such as an amateur television (ATV) operator, that transmits video content and audio content via radio waves directly from a transmitter on the earth ...
. Specialized receivers for the PRO channel are generally only sold to broadcast professionals. This sub-carrier is at 6.5x horizontal sync.
MTS signals are indicated to the television receiver by adding a 15.734 kHz pilot tone
An aircraft pilot or aviator is a person who controls the flight of an aircraft by operating its directional flight controls. Some other aircrew members, such as navigators or flight engineers, are also considered aviators, because they a ...
to the signal.
The MTS pilot is locked or derived from the horizontal sync signal used to lock the video display. Variations in phase or frequency of the horizontal sync are therefore transferred to the audio. UHF transmitters in use in 1984 generally had significant phase errors introduced in this signal making the transmission of stereo audio on UHF stations of that time nearly impossible. Later refinements in UHF transmitters minimized these effects and allowed stereo transmission for those stations.
Most FM broadcast receivers are capable of receiving the audio portion of NTSC Channel 6 at 87.75 MHz, but only in monaural
Monaural or monophonic sound reproduction (often shortened to mono) is sound intended to be heard as if it were emanating from one position. This contrasts with stereophonic sound or ''stereo'', which uses two separate audio channels to reproduc ...
. Because the pilot tone frequency at 15.734 kHz is different from that of the ordinary FM band (19 kHz), such radios cannot decode MTS.
Real-world performance
In ideal circumstances, MTS Stereo is better in performance than standard VHF FM stereo. In both FM Stereo and MTS the L-R subchannel is AM double-sideband modulated. AM is known to be susceptible to interference and noise reduction to the sub-channel aids in the improvement of SNR over standard FM broadcast. The sub-channel information is dbx-encode
The Encyclopedia of DNA Elements (ENCODE) is a public research project which aims to identify functional elements in the human genome.
ENCODE also supports further biomedical research by "generating community resources of genomics data, software ...
d to improve the audio with typical SNR greater than 50 dB. By adding noise reduction to the sub-channel only, complete mono compatibility was maintained. Viewers who owned mono TV sets would hear normal audio, only limited to 15 kHz bandwidth.
The original specifications called for a brick wall elliptical filter in each of the audio channels prior to encoding. The cutoff frequency of this filter was 15 kHz to prevent any horizontal sync interference (15.734 kHz) from being encoded in the audio. Manufacturers of modulators, however, used lower cutoff filters as they saw fit, also reducing the cost of audio filters. Typically, they chose 14 kHz although some used filters as low as 12.5 kHz. The elliptical filter was chosen for having the greatest bandwidth with the lowest phase distortion at the cutoff frequency. In comparison, standard FM modulators filter the audio at slightly higher frequencies but still must protect the 19 kHz pilot signal. The filter used during EIA/FCC testing had a characteristic that was −60 dB at 15.5 kHz. As transformer audio coupling was common at that time, the lower frequency limit was set to 50 Hz although modulators without transformer inputs were flat down to at least 20 Hz.
Typical separation was better than 35 dB. However, level matching between channels was essential to achieve this specification. Left and Right audio levels needed to be matched within less than 0.1 dB to achieve the separation stated.
Maintaining the phase stability of the horizontal sync is essential to good audio in the decode process. During transmission, the phase of the horizontal sync could vary with picture and chroma levels. ICPM (Incidental Carrier Phase Modulation), a measure of transmitted phase stability, needs to be less than 4.5% for best audio sub channel decoding. This was more of a problem with UHF transmitters of the day. Multi-cavity klystron RF amplifiers of that time typically had an ICPM above 7%. This made UHF transmission of MTS stereo impossible. Later UHF transmitter designs imporved ICPM performance and allowed MTS stereo transmission.
Licensing
Because of the use of dbx companding
In telecommunication and signal processing, companding (occasionally called compansion) is a method of mitigating the detrimental effects of a channel with limited dynamic range. The name is a portmanteau of the words compressing and expanding, ...
, every TV device that decoded MTS originally required the payment of royalties
A royalty payment is a payment made by one party to another that owns a particular asset, for the right to ongoing use of that asset. Royalties are typically agreed upon as a percentage of gross or net revenues derived from the use of an asset o ...
—first to dbx, Inc.
dbx, Inc. is an American manufacturer of professional audio recording equipment owned by Harman International, a subsidiary of South Korea-based company Samsung Electronics. It was founded by David E. Blackmer in 1971.
The original company go ...
, then to THAT Corporation
''That'' is an English language word used for several grammatical purposes. These include use as an adjective, conjunction, pronoun, adverb, and intensifier; it has distance from the speaker, as opposed to words like ''this''. The word did not o ...
which was spun off from dbx in 1989 and acquired its MTS patents in 1994; however, those patents expired worldwide in 2004.dbx-TV Timeline (THAT Corporation)
Though THAT now owns some patents related to digital implementations of MTS, a letter from THAT to the National Telecommunications and Information Administration
The National Telecommunications and Information Administration (NTIA) is an agency of the United States Department of Commerce that serves as the President's principal adviser on telecommunications policies pertaining to the United States' ec ...
in 2007 confirms that no license is required from THAT for all analog and some digital implementations of MTS.
Adoption
Several nations outside North America using the NTSC
The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...
standard adopted the MTS format for their analog systems, including Chile
Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...
, Colombia
Colombia (, ; ), officially the Republic of Colombia, is a country in South America with insular regions in North America—near Nicaragua's Caribbean coast—as well as in the Pacific Ocean. The Colombian mainland is bordered by the Car ...
, Taiwan
Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...
and the Philippines
The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no),
* bik, Republika kan Filipinas
* ceb, Republika sa Pilipinas
* cbk, República de Filipinas
* hil, Republ ...
, along with Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
, with their own domestic NTSC variant. Two countries, Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
and Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
, used the MTS standard with the alternate PAL
Phase Alternating Line (PAL) is a colour encoding system for analogue television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...
standard.
See also
* NICAM
Near Instantaneous Companded Audio Multiplex (NICAM) is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks.Croll, M.G., Osborne, D.W. and Spi ...
* Zweikanalton
Zweikanalton ("two-channel sound") or A2 Stereo, is an analog television sound transmission system used in Germany, Austria, Australia, Switzerland, Netherlands and some other countries that use or used PAL-B or PAL-G. TV3 Malaysia formerly used ...
* EIAJ MTS
EIAJ MTS is a multichannel television sound standard created by the EIAJ.
Bilingual and stereo sound television programs started being broadcast in Japan in October 1978 using a " FM-FM" system originally developed by NHK Technical Research La ...
References
Sources
* Alan Skierkiewicz (November 1985), "Stereo one year later", Television Broadcast, p. 76
{{DEFAULTSORT:Multichannel Television Sound
Broadcast engineering
Sound
Television technology