Satellite subcarrier audio is audio transmitted by way of

satellite A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...

that uses a separate analog or

digital Digital usually refers to something using discrete digits, often binary digits. Businesses *Digital bank, a form of financial institution *Digital Equipment Corporation (DEC) or Digital, a computer company *Digital Research (DR or DRI), a software ...

signal carried on a main radio transmission (usually video) on a specific satellite

transponder In telecommunications, a transponder is a device that, upon receiving a signal, emits a different signal in response. The term is a blend of ''transmitter'' and ''responder''. In air navigation or radio frequency identification, a flight trans ...

. More technically, it is an already-modulated signal, which is then modulated into another signal of higher frequency and bandwidth. In a more general sense, satellite subcarrier audio is an early form of

satellite radio Satellite radio is defined by the International Telecommunication Union (ITU)'s ITU Radio Regulations (RR) as a '' broadcasting-satellite service''. The satellite's signals are broadcast nationwide, across a much wider geographical area than te ...

not intended for the consumer market but was initially unencrypted, thus receivable to satellite hobbyists. Original analog video only has one channel per transponder, with

subcarrier A subcarrier is a sideband of a radio frequency carrier wave, which is modulated to send additional information. Examples include the provision of colour in a black and white television system or the provision of stereo in a monophonic radio bro ...

s for audio and automatic transmission identification service ATIS. Non-multiplexed

radio station Radio broadcasting is the broadcasting of audio (sound), sometimes with related metadata, by radio waves to radio receivers belonging to a public audience. In terrestrial radio broadcasting the radio waves are broadcast by a land-based rad ...

s can also travel in

single channel per carrier Single channel per carrier (SCPC) refers to using a single signal at a given frequency and bandwidth. Most often, this is used on broadcast satellites to indicate that radio stations are not multiplexed as subcarriers onto a single video ca ...

(SCPC) mode, with multiple carriers (analog or digital) per transponder. This allows each station to transmit directly to the satellite, rather than paying for a whole transponder, or using

landline A landline is a physical telephone connection that uses metal wires or optical fiber from the subscriber's premises to the network, allowing multiple phones to operate simultaneously on the same phone number. It is also referred to as plain old ...

s to send it to an

earth station A ground station, Earth station, or Earth terminal is a terrestrial radio station designed for extraplanetary telecommunication with spacecraft (constituting part of the ground segment of the spacecraft system), or reception of radio waves fro ...

for multiplexing with other stations.

Analog subcarriers

Satellite subcarrier audio was initially transmitted in analog form. This method of audio transmission was first employed by Fujitsu in 1973 as part of a data line between the United States and Spain. By the early 1980s, the use of analog subcarriers for radio network distribution had become well-established.

Standard subcarrier audio

Initially, satellite subcarrier audio was tuned using commercial receivers or consumer-grade TVRO "big dish" satellite receivers. The audio ranged in frequency from 5.0 to 8.5

MHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base u ...

for both left and right audio channels. Fine tuning options included monaural and discrete stereo tuning with three bandwidth modes: narrow (130 kHz), normal (280 kHz) and wide (500 kHz).

Single channel per carrier (analog SCPC)

Single channel per carrier (SCPC) refers to using a single

signal A signal is both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology. In ...

at a given

frequency Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...

and

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 ...

. Most often, this is used on broadcast satellites to indicate that

s are not

multiplexed In telecommunications and computer networking, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource— ...

s onto a single video carrier, but instead independently share a

. It may also be used on other

communications satellite A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a Transponder (satellite communications), transponder; it creates a communication channel between a source transmitter and a Rad ...

s, or occasionally on non-satellite transmissions. In an SCPC system, satellite bandwidth is dedicated to a single source. Analog SCPC subcarrier audio is received using dedicated satellite receivers. SCPC audio receivers tune a frequency range of 50 to 90 MHz with both wide and narrow bandwidth options. Receivers in the hobbyist price range included the Heil SC-One and the Universal Electronics SCPC-100 and SCPC-200.

FM Squared (FM²)

The FM Squared satellite audio format was developed in 1986 by Wegener Communications and Subcarrier Systems (later SpaceCom Systems, Inc.). FM Squared is a method of transmitting analog satellite audio where video would normally be transmitted on a satellite transponder. FM Squared was once used to distribute

Muzak Muzak is an American brand of background music played in retail stores and other public establishments owned by Mood Media. The name ''Muzak'', a blend of music and the popular camera brand name Kodak, has been in use since 1934 and has been ...

and similar "business" music (sometimes referred to as

elevator music Elevator music (also known as Muzak, piped music, or lift music) is a type of background music played in elevators, in rooms where many people come together for reasons other than listening to music, and during telephone calls when placed on ho ...

) to retailers. FM Squared audio receivers tune a frequency range of 100 kHz to 9 MHz. Receivers that fell within the hobbyist price range included the Universal Electronics SC-50.

Digital subcarriers

Although not widely used until the early 2000s, digital subcarrier audio has existed almost as long as its analog technology counterpart. In 1972, the

BBC The British Broadcasting Corporation (BBC) is a British public service broadcaster headquartered at Broadcasting House in London, England. Originally established in 1922 as the British Broadcasting Company, it evolved into its current sta ...

deployed a digital audio transmission system linking their broadcast center to their remote transmitters. This technology wasn't applied to satellite communications, however, until the early 1980s.

DATS and SEDAT

The first widespread digital satellite audio distribution system was Digital Audio Transmission System (DATS). DATS was developed in 1982 by Scientific Atlanta. The DATS distribution system was first used by the largest U.S. radio networks such as

Westwood One Westwood One, Inc. is an American radio network owned by Cumulus Media. The company syndicates talk, music, and sports programming. The company takes its name from an earlier network also named Westwood One, a company founded in 1976. The co ...

, ABC Radio Networks and

NBC The National Broadcasting Company (NBC) is an American commercial broadcast television and radio network serving as the flagship property of the NBC Entertainment division of NBCUniversal, a subsidiary of Comcast. It is one of NBCUniversal's ...

. The DATS system transmitted up to four 15 kHz analog audio channels at a data rate of 1.544

Mbit/s In telecommunications, data transfer rate is the average number of bits (bitrate), characters or symbols (baudrate), or data blocks per unit time passing through a communication link in a data-transmission system. Common data rate units are multi ...

(384 kbit/s each) between their originating radio studios and a C-band earth station where they were de-multiplexed, re-multiplexed, and uplinked with additional digital audio channels using BPSK digital modulation. The 15 kHz channels had a dynamic range of 81 dB which was suitable for FM broadcasting. The system could also support up to twice as many 7.5 kHz channels suitable for AM broadcast. DATS was later superseded by the Spectrum Efficient Digital Audio Transmission (SEDAT) satellite audio distribution system. SEDAT allows more audio channels to be carried in the same frequency range as DATS. SEDAT, also developed by Scientific Atlanta, was primarily used by ABC Radio Networks. SEDAT transmissions ended in 2001.

Digital SCPC and MCPC

As digital subcarrier audio encoding and modulation methods have matured, less-expensive "standard" systems of satellite audio distribution have developed. This trend started with the emergence of

VSAT A very-small-aperture terminal (VSAT) is a two-way satellite ground station with a satellite dish, dish antenna that is smaller than 3.8 meters. The majority of VSAT antennas range from 75 cm to 1.2 m. Bit rates, in most cases, range from 4 ...

technology in 1986 and was further supplanted by leased space on DBS systems such as

DirecTV DirecTV, LLC is an American Multichannel television in the United States, multichannel video programming distributor based in El Segundo, California. Originally launched on June 17, 1994, its primary service is a digital Satellite television, s ...

and

Dish Network DISH Network L.L.C., often referred to as DISH, an abbreviation for Digital Sky Highway, is an American provider of satellite television and IPTV services and wholly owned subsidiary of EchoStar Corporation. The company was originally establ ...

. The two ''de facto'' methods for digital satellite audio transmission are digital

and multiple channel per carrier

multiplexing In telecommunications and computer networking, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource� ...

. In digital radio systems, several variable bit-rate data streams are multiplexed together to a fixed bitrate transport stream by means of statistical multiplexing. This makes it possible to transfer several video and audio channels simultaneously over the same frequency channel, together with various services. On communications satellites that carry broadcast television networks and radio networks, this is known as multiple channel per carrier or MCPC. Where multiplexing is not practical (such as where there are different sources using a single transponder), single channel per carrier mode (SCPC) is used. Digital SCPC differs from the older analog SCPC transmission method in that a digital SCPC signal carries more than just a single audio channel (two are used) but also coding and decoding information, ancillary and control data, and network identification data. Digital SCPC and MCPC subcarrier transmissions use satellite broadcast standards such as

DVB-S Digital Video Broadcasting – Satellite (DVB-S) is the original DVB standard for satellite television and dates from 1995, in its first release, while development lasted from 1993 to 1997. The first commercial applications were by Canal+ in ...

and its successor

DVB-S2 Digital Video Broadcasting - Satellite - Second Generation (DVB-S2) is a digital television broadcast standard that has been designed as a successor for the popular DVB-S system. It was developed in 2003 by the Digital Video Broadcasting Proj ...

along with

MPEG-2 MPEG-2 (a.k.a. H.222/H.262 as was defined by the ITU) is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods ...

and

MPEG-4 MPEG-4 is a group of international standards for the compression of digital audio and visual data, multimedia systems, and file storage formats. It was originally introduced in late 1998 as a group of audio and video coding formats and related ...

compression formats, respectively. BPSK modulation has been replaced with newer modulation schemes such as

QPSK Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency carrier wave. The modulation is accomplished by varying the sine and cosine inputs at a precise time. It is ...

(quadrature phase-shift keying).

StarGuide

StarGuide was the second-generation system of digital audio distribution via satellite. Many of the largest U.S. radio networks upgraded from or supplanted DATS/SEDAT audio feeds with StarGuide II and III audio receivers. The StarGuide platform is a proprietary MCPC digital audio distribution system that uses proprietary MX3 multiplexing technology. The StarGuide II receiver handles data rates from 0.512 to 6.144 Mbit/s (in MX3 mode) and up to 8.192 Mbit/s in normal mode. The StarGuide III receiver can handle data rates up to 25 Mbit/s and is capable of a larger number of data and code rates than its predecessor. Both the StarGuide II and III receivers can use proprietary StarGuide Service Module expansion cards, including the ability to interface with

local area network A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, campus, or building, and has its network equipment and interconnects locally managed. LANs facilitate the distribution of da ...

s (LAN) using 10/100 Ethernet connections.

X-Digital (XDS) format

The X-Digital Systems format is (as of 2011) the newest generation of digital satellite subcarrier audio technology used by the large radio networks in the United States. In 2007, X-Digital Systems acquired specific assets and patent licensing of StarGuide Digital Networks technology from DG FastChannel, Inc. The X-Digital Systems platform has been deployed by

Clear Channel Communications iHeartMedia, Inc., or CC Media Holdings, Inc., is an American mass media corporation headquartered in San Antonio, Texas. It is the holding company of iHeartCommunications, Inc., formerly Clear Channel Communications, Inc., a company founded by ...

, Premiere Networks (now an iHeartMedia subsidiary) and

Citadel Broadcasting Citadel Broadcasting Corporation was a Las Vegas, Nevada-based broadcast holding company founded and developed by Larry Wilson. Citadel owned 243 radio stations across the United States and was the third-largest radio station owner in the count ...

(who also owns the former ABC Radio Networks).

External links

ATX Networks website (parent company of the X-Digital Systems format)

References

{{reflist Satellite radio