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A wireless microphone, or cordless microphone, is a
microphone
A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public ...
without a physical cable connecting it directly to the sound recording or amplifying equipment with which it is associated. Also known as a radio microphone, it has a small, battery-powered
radio transmitter
In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the ...
in the microphone body, which transmits the audio signal from the microphone by
radio wave
Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (short ...
s to a nearby receiver unit, which recovers the audio. The other audio equipment is connected to the receiver unit by cable. In one type the transmitter is contained within the handheld microphone body. In another type the transmitter is contained within a separate unit called a "bodypack", usually clipped to the user's belt or concealed under their clothes. The bodypack is connected by wire to a "lavalier microphone" or "lav" (a small microphone clipped to the user's lapel), a headset or earset microphone, or another wired microphone. Most bodypack designs also support a wired instrument connection (e.g., to a guitar). Wireless microphones are widely used in the
entertainment industry
Entertainment is a form of activity that holds the attention and Interest (emotion), interest of an audience or gives pleasure and delight. It can be an idea or a task, but is more likely to be one of the activities or events that have dev ...
,
television broadcasting
A television network or television broadcaster is a telecommunications network for distribution of television program content, where a central operation provides programming to many television stations or pay television providers. Until the mid-1 ...
, and
public speaking
Public speaking, also called oratory or oration, has traditionally meant the act of speaking face to face to a live audience. Today it includes any form of speaking (formally and informally) to an audience, including pre-recorded speech deliver ...
to allow public speakers, interviewers, performers, and entertainers to move about freely while using a microphone without requiring a cable attached to the microphone.
Wireless microphones usually use the
VHF or
UHF frequency bands since they allow the transmitter to use a small unobtrusive antenna. Cheap units use a fixed frequency but most units allow a choice of several frequency channels, in case of
interference
Interference is the act of interfering, invading, or poaching. Interference may also refer to:
Communications
* Interference (communication), anything which alters, modifies, or disrupts a message
* Adjacent-channel interference, caused by extr ...
on a channel or to allow the use of multiple microphones at the same time.
FM modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informatio ...
is usually used, although some models use
digital modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informatio ...
to prevent unauthorized reception by scanner radio receivers; these operate in the 900 MHz, 2.4 GHz or 6 GHz
ISM band
The ISM radio bands are portions of the radio spectrum reserved internationally for industrial, scientific and medical (ISM) purposes, excluding applications in telecommunications.
Examples of applications for the use of radio frequency (RF) ener ...
s. Some models use
antenna diversity
Antenna diversity, also known as space diversity or spatial diversity, is any one of several wireless diversity schemes that uses two or more antennas to improve the quality and reliability of a wireless link. Often, especially in urban and ind ...
(two antennas) to prevent
null
Null may refer to:
Science, technology, and mathematics Computing
* Null (SQL) (or NULL), a special marker and keyword in SQL indicating that something has no value
* Null character, the zero-valued ASCII character, also designated by , often use ...
s from interrupting transmission as the performer moves around. A few low cost (or specialist) models use
infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
light, although these require a direct line of sight between microphone and receiver.
History
Various individuals and organizations claim to be the inventors of the wireless microphone.
From about 1945 there were schematics and hobbyist kits offered in ''
Popular Science
''Popular Science'' (also known as ''PopSci'') is an American digital magazine carrying popular science content, which refers to articles for the general reader on science and technology subjects. ''Popular Science'' has won over 58 awards, incl ...
'' and ''
Popular Mechanics
''Popular Mechanics'' (sometimes PM or PopMech) is a magazine of popular science and technology, featuring automotive, home, outdoor, electronics, science, do-it-yourself, and technology topics. Military topics, aviation and transportation o ...
'' for making a wireless microphone that would transmit the voice to a nearby radio.
Figure skater
Figure skating is a sport in which individuals, pairs, or groups perform on figure skates on ice. It was the first winter sport to be included in the Olympic Games, when contested at the 1908 Olympics in London. The Olympic disciplines are me ...
and
Royal Air Force
The Royal Air Force (RAF) is the United Kingdom's air and space force. It was formed towards the end of the First World War on 1 April 1918, becoming the first independent air force in the world, by regrouping the Royal Flying Corps (RFC) and ...
flight engineer Reg Moores developed a radio microphone in 1947 that he first used in the
Tom Arnold Tom Arnold may refer to:
* Tom Arnold (actor) (born 1959), American actor
* Tom Arnold (economist) (born 1948), Irish CEO of Concern Worldwide
* Tom Arnold (footballer) (1878–?), English footballer
* Tom Arnold (literary scholar) (1823–1900), ...
production "Aladdin on Ice" at
Brighton
Brighton () is a seaside resort and one of the two main areas of the City of Brighton and Hove in the county of East Sussex, England. It is located south of London.
Archaeological evidence of settlement in the area dates back to the Bronze A ...
's sports stadium from September 1949 through the Christmas season. Moores affixed the wireless transmitter to the costume of the character Abanazar, and it worked perfectly. Moores did not patent his idea, as he was illegally using the radio frequency 76 MHz. The producers of the ice show decided that they would not continue using the device; they would rather hire actors and singers to perform into hidden microphones to "dub" the voices of the other ice skaters, who would thus be free to concentrate on their skating. In 1972 Moores donated his 1947 prototype to the
Science Museum
A science museum is a museum devoted primarily to science. Older science museums tended to concentrate on static displays of objects related to natural history, paleontology, geology, industry and industrial machinery, etc. Modern trends in mu ...
in London.
Herbert "Mac" McClelland, founder of McClelland Sound in
Wichita, Kansas
Wichita ( ) is the largest city in the U.S. state of Kansas and the county seat of Sedgwick County, Kansas, Sedgwick County. As of the 2020 United States census, 2020 census, the population of the city was 397,532. The Wichita metro area had ...
, fabricated a wireless microphone to be worn by baseball umpires at major league games broadcast by NBC from
Lawrence–Dumont Stadium
Lawrence–Dumont Stadium, previously known as Lawrence Stadium, was a baseball stadium in Wichita, Kansas, United States. It was located on the northwest corner of McLean Boulevard and Maple Street, along the west bank of the Arkansas River, in ...
in 1951. The transmitter was strapped to the umpire's back. Mac's brother was
Harold M. McClelland, the chief communications architect of the U.S. Air Force.
Shure Brothers
Shure Incorporated is an American audio products corporation. It was founded by Sidney N. Shure in Chicago, Illinois, in 1925 as a supplier of radio parts kits. The company became a consumer and professional audio-electronics manufacturer of mi ...
claims that its "Vagabond" system from 1953 was the first "wireless microphone system for performers."
Its field of coverage was a circle of "approximately 700 square feet", which corresponds to a line-of-sight distance of only from the receiver.
[
In 1957, the German audio equipment manufacturer ]Sennheiser
Sennheiser electronic GmbH & Co. KG (, ) is a German privately held audio company specializing in the design and production of a wide range of high fidelity products, including microphones, headphones, telephone accessories and aviation headse ...
, at that time called Lab W, working with the German broadcaster Norddeutscher Rundfunk
Norddeutscher Rundfunk (NDR; ''Northern German Broadcasting'') is a public broadcasting, public radio and television broadcaster, based in Hamburg. In addition to the city-state of Hamburg, NDR broadcasts for the German states of Lower Saxony, M ...
(NDR), exhibited a wireless microphone system. From 1958 the system was marketed through Telefunken
Telefunken was a German radio and television apparatus company, founded in Berlin in 1903, as a joint venture of Siemens & Halske and the ''Allgemeine Elektrizitäts-Gesellschaft'' (AEG) ('General electricity company').
The name "Telefunken" app ...
under the name of Mikroport. The pocket-sized Mikroport incorporated a dynamic moving-coil cartridge microphone with a cardioid pickup pattern. It transmitted at 37 MHz with a specified range of .
The first recorded patent for a wireless microphone was filed by Raymond A. Litke
Raymond A. Litke (1920-1986) was an American electronic engineer, the inventor of a practical wireless microphone, and the first to patent the wireless microphone. He was born and raised on a farm near Alma, Kansas, but spent most of his adult lif ...
, an American electrical engineer with Educational Media Resources and San Jose State College
San José State University (San Jose State or SJSU) is a public university in San Jose, California. Established in 1857, SJSU is the oldest public university on the West Coast and the founding campus of the California State University (CSU) sy ...
, who invented a wireless microphone in 1957 to meet the multimedia needs for television, radio, and classroom instruction. His U.S. patent number 3134074 was granted in May 1964. Two microphone types were made available for purchase in 1959: hand-held and lavalier. The main transmitter module was a cigar-sized device which weighed . Vega Electronics Corporation manufactured the design in 1959, producing it as a product called the Vega-Mike. The device was first used by the broadcast media at the 1960 Democratic and Republican National Conventions. It allowed television reporters to roam the floor of the convention to interview participants, including presidential candidates John F. Kennedy
John Fitzgerald Kennedy (May 29, 1917 – November 22, 1963), often referred to by his initials JFK and the nickname Jack, was an American politician who served as the 35th president of the United States from 1961 until his assassination ...
and Richard Nixon
Richard Milhous Nixon (January 9, 1913April 22, 1994) was the 37th president of the United States, serving from 1969 to 1974. A member of the Republican Party, he previously served as a representative and senator from California and was ...
.
Introduced in 1958, the Sony
, commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professional ...
CR-4 wireless microphone was being recommended as early as 1960 for theatre performances and nightclub acts. Animal trainers at Marineland of the Pacific
Marineland of the Pacific was a public oceanarium and tourist attraction located on the Palos Verdes Peninsula coast in Los Angeles County, California, Los Angeles County, California. Architect William Pereira designed the main structure. It wa ...
in California were wearing the $250 device for performances in 1961. The 27.12 MHz solid-state FM transmitter was capable of fitting into a shirt pocket. Said to be effective out to , it mounted a flexible dangling antenna and a detachable dynamic microphone. The tube-based receiver incorporated a carrying drawer for the transmitter and a small monitor loudspeaker with volume control.
Another German equipment manufacturer, Beyerdynamic, claims that the first wireless microphone was invented by Hung C. Lin. Called the "transistophone", it went into production in 1962. The first time that a wireless microphone was used to record sound during filming of a motion picture was allegedly on Rex Harrison
Sir Reginald Carey "Rex" Harrison (5 March 1908 – 2 June 1990) was an English actor. Harrison began his career on the stage in 1924. He made his West End debut in 1936 appearing in the Terence Rattigan play ''French Without Tears'', in what ...
in the 1964 film ''My Fair Lady'', through the efforts of Academy Award
The Academy Awards, better known as the Oscars, are awards for artistic and technical merit for the American and international film industry. The awards are regarded by many as the most prestigious, significant awards in the entertainment ind ...
-winning Hollywood sound engineer George Groves.
Wider dynamic range came with the introduction of the first compander
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, ...
wireless microphone, offered by Nady Systems in 1976. Todd Rundgren
Todd Harry Rundgren (born June 22, 1948) is an American multi-instrumentalist, singer, songwriter, multimedia artist, sound engineer and record producer who has performed a diverse range of styles as a solo artist and as a member of the band Ut ...
and the Rolling Stones
The Rolling Stones are an English rock band formed in London in 1962. Active for six decades, they are one of the most popular and enduring bands of the rock era. In the early 1960s, the Rolling Stones pioneered the gritty, rhythmically d ...
were the first popular musicians to use these systems live in concert. Kate Bush
Catherine Bush (born 30 July 1958) is an English singer, songwriter, record producer and dancer. In 1978, at the age of 19, she topped the UK Singles Chart for four weeks with her debut single "Wuthering Heights (song), Wuthering Heights", ...
is regarded as the first artist to have had a headset with a wireless microphone built for use in music. For her '' Tour of Life'' in 1979 she had a compact microphone combined with a self-made construction of wire clothes hanger
A clothes hanger, coat hanger, or coathanger, is a hanging device in the shape/contour of:
* Human shoulders designed to facilitate the hanging of a coat, jacket, sweater, shirt, blouse or dress in a manner that prevents wrinkles, with a l ...
s, to free her hands for expressionist dance performances. Her idea was adopted for live performance by other artists such as Madonna
Madonna Louise Ciccone (; ; born August 16, 1958) is an American singer-songwriter and actress. Widely dubbed the " Queen of Pop", Madonna has been noted for her continual reinvention and versatility in music production, songwriting, a ...
and Peter Gabriel
Peter Brian Gabriel (born 13 February 1950) is an English musician, singer, songwriter, record producer, and activist. He rose to fame as the original lead singer of the progressive rock band Genesis. After leaving Genesis in 1975, he launched ...
.
Nady joined CBS, Sennheiser and Vega in 1996 to receive a joint Emmy Award
The Emmy Awards, or Emmys, are an extensive range of awards for artistic and technical merit for the American and international television industry. A number of annual Emmy Award ceremonies are held throughout the calendar year, each with the ...
for "pioneering hedevelopment of the broadcast wireless microphone".
Advantages and disadvantages
The advantages are:
*Greater freedom of movement for the artist or speaker
*Avoidance of cabling problems common with wired microphones, caused by constant moving and stressing the cables
*Reduction of cable "trip hazards" in the performance space
*Galvanic isolation
Galvanic isolation is a principle of isolating functional sections of electrical systems to prevent current flow; no direct conduction path is permitted.John Huntington ''Show Networks and Control Systems: Formerly Control Systems for Live ...
of microphone, avoiding ground loops between microphone and other electrical instruments on stage
The disadvantages are:
*Lower sound quality
*Sometimes limited range (a wired balanced XLR microphone
A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public ...
can run up to 300 ft or 100 meters). Some wireless systems have a shorter range, while more expensive models can exceed that distance.
*Possible interference with or, more often, from other radio equipment or other radio microphones, though models with many frequency-synthesized switch-selectable channels are now plentiful and cost effective.
*Operation time is limited relative to battery life; it is shorter than a normal condenser microphone due to greater drain on batteries from transmitting circuitry, and from circuitry giving extra features, if present.
*Noise or dead spots (places where it doesn't work, especially in non-diversity systems)
*Limited number of operating microphones at the same time and place, due to the limited number of radio channels (frequencies).
*Higher cost in proportion to fewer other features
Techniques
The professional models transmit in VHF or UHF radio frequency and have 'true' diversity reception
In telecommunications, a diversity scheme refers to a method for improving the reliability of a message signal by using two or more Channel (communications), communication channels with different characteristics. Diversity is mainly used in radio ...
(two separate receiver modules, each with its own antenna), which eliminates dead spots (caused by phase cancellation) and the effects caused by the reflection of the radio waves on walls and surfaces in general. (See antenna diversity
Antenna diversity, also known as space diversity or spatial diversity, is any one of several wireless diversity schemes that uses two or more antennas to improve the quality and reliability of a wireless link. Often, especially in urban and ind ...
).
Another technique used to improve the sound quality (actually, to improve the dynamic range), is 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, ...
. Nady Systems, Inc. was the first to offer this technology in wireless microphones in 1976, which was based on the patent obtained by company founder John Nady.
Some models have adjustable gain
Gain or GAIN may refer to:
Science and technology
* Gain (electronics), an electronics and signal processing term
* Antenna gain
* Gain (laser), the amplification involved in laser emission
* Gain (projection screens)
* Information gain in de ...
on the microphone itself to be able to accommodate different level sources, such as loud instruments or quiet voices. Adjustable gain helps to avoid clipping
Clipping may refer to:
Words
* Clipping (morphology), the formation of a new word by shortening it, e.g. "ad" from "advertisement"
* Clipping (phonetics), shortening the articulation of a speech sound, usually a vowel
* Clipping (publications) ...
and maximize signal to noise ratio.
Some models have adjustable squelch
In telecommunications, squelch is a circuit function that acts to suppress the audio (or video) output of a receiver in the absence of a strong input signal. Essentially, squelch is a specialized type of noise gate designed to suppress weak s ...
, which silences the output when the receiver does not get a strong or quality signal from the microphone, instead of reproducing noise. When squelch is adjusted, the threshold of the signal quality or level is adjusted.
Products
AKG Acoustics, Audio Ltd, Audio-Technica
(stylized as audio-technica) is a Japanese company that designs and manufactures professional microphones, headphones, turntables, phonographic magnetic cartridges, and other audio equipment.
Company history
Audio-Technica was established ...
, Electro-Voice, Lectrosonics, MIPRO
MIPRO Electronics Co., Ltd. (), established in 1995, is an ISO-9001 certified Taiwan-based company that designs and manufactures wireless microphones, portable wireless public address ( PA) and other wireless audio equipment for consumer, profess ...
, Nady Systems, Inc, Samson Technologies
Samson (; , '' he, Šīmšōn, label= none'', "man of the sun") was the last of the judges of the ancient Israelites mentioned in the Book of Judges (chapters 13 to 16) and one of the last leaders who "judged" Israel before the institution o ...
, Sennheiser
Sennheiser electronic GmbH & Co. KG (, ) is a German privately held audio company specializing in the design and production of a wide range of high fidelity products, including microphones, headphones, telephone accessories and aviation headse ...
, Shure
Shure Incorporated is an American audio products corporation. It was founded by Sidney N. Shure in Chicago, Illinois, in 1925 as a supplier of radio parts kits. The company became a consumer and professional audio-electronics manufacturer of mi ...
, Sony
, commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professional ...
, Wisycom and Zaxcom are all major manufacturers of wireless microphone systems. They have made significant advances in dealing with many of the disadvantages listed above. For example, while there is a limited band in which the microphones may operate, several high-end systems can consist of over 100 different microphones operating simultaneously. However, the ability to have more microphones operating at the same time increases the cost due to component specifications, design and construction. That is one reason for such large price differences between different series of wireless systems.
Generally there are three wireless microphone types: handheld, plug-in and bodypack:
*Handheld looks like a 'normal' wired microphone, may have a bigger body to accommodate the transmitter
In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna (radio), antenna. The transmitter itself generates a radio frequency alternating current, which i ...
and battery pack.
*Plug-in, plug-on, slot-in, or cube-style transmitters attach to the bottom of a standard microphone, thus converting it to wireless operation (see below).
*Bodypack is a small box housing the transmitter and battery pack, but not the microphone itself. It is attachable to clothing or on the body and has a wire going into a headset, a lavalier microphone
A lavalier microphone or lavalier (also known as a lav, lapel mic, clip mic, body mic, collar mic, neck mic or personal mic) is a small microphone used for television, theater, and public speaking applications to allow hands-free operation. They a ...
or a guitar
The guitar is a fretted musical instrument that typically has six strings. It is usually held flat against the player's body and played by strumming or plucking the strings with the dominant hand, while simultaneously pressing selected stri ...
.
Several manufacturers including Sennheiser, AKG, Nady Systems, Lectrosonics and Zaxcom offer a plug-in transmitter for existing wired microphones, which plugs into the XLR output of the microphone and transmits to the manufacturer's standard receiver. This offers many of the benefits of an integrated system, and also allows microphone types (of which there may be no wireless equivalent) to be used without a cable. For example, a television, or film, sound production engineer may use a plug-in transmitter to enable wireless transmission of a highly directional rifle (or "shotgun") microphone, removing the safety hazard of a cable connection and permitting the production engineer greater freedom to follow the action. Plug-in transmitters also allow the conversion of vintage microphone types to cordless operation. This is useful where a vintage microphone is needed for visual or other artistic reasons, and the absence of cables allows for rapid scene changes and reducing trip hazards. In some cases these plug-in transmitters can also provide 48 volt phantom power
Phantom power, in the context of professional audio equipment, is DC electric power transmitted through microphone cables to operate microphones that contain active electronic circuitry.
It is best known as a convenient power source for con ...
allowing the use of condenser microphone
A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public ...
types. DC-DC converter
A DC-to-DC converter is an electronic circuit or electromechanical device that converts a source of direct current (DC) from one voltage level to another. It is a type of electric power converter. Power levels range from very low (small batteries) ...
circuitry within the transmitter is used to multiply the battery supply, which may be three volts or less, up to the required 48 volts.
Receivers
There are many types of receiver.
True Diversity receivers have two radio modules and two antennas.
Diversity receivers have one radio module and two antennas, although some times the second antenna may not be obviously visible.
Non-diversity receivers have only one antenna.
Receivers are commonly housed in a half-rack configuration, so that two can be mounted together in a rack system (that is to say the receiver is enclosed in a box 1U high and half-width, so two receivers can be installed in 1U). For large complex multi channel radio microphone systems, as used in broadcast television studio
A television studio, also called a television production studio, is an installation room in which video productions take place, either for the production of live television and its recording onto video tape or other media such as SSDs, or for ...
s and musical theatre productions, modular receiver systems with several (commonly six or eight) true diversity receivers slotting into a rack-mounted mainframe housing are available. Several mainframes may be used together in a rack to supply the number of receivers required. In some musical theatre productions, systems with forty or more radio microphones are not unusual.
Receivers specifically for use with video cameras are often mounted in a bodypack configuration, typically with a hotshoe mount to be fitted onto the hotshoe of the camcorder. Small true diversity receivers which slot into a special housing on many professional broadcast standard video cameras are produced by manufacturers including Sennheiser, Lectrosonics and Sony
, commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professional ...
. For less demanding or more budget conscious video applications small non-diversity receivers are common. When used at relatively short operating distances from the transmitter this arrangement gives adequate and reliable performance.
Bandwidth and spectrum
Almost all wireless microphone systems use wide band FM modulation, requiring approximately 200 kHz of bandwidth. Because of the relatively large bandwidth requirements, wireless microphone use is effectively restricted to VHF and above.
Many older wireless microphone systems operate in the VHF part of the electromagnetic spectrum. Systems operating in this range are often crystal-controlled, and therefore operate on a single frequency. However, if this frequency is chosen properly, the system will be able to operate for years without any problems.
Most modern wireless microphone products operate in the UHF television band, however. In the United States, this band extends from 470 MHz to 614 MHz. In 2010 the 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 ...
issued new regulations on the operations of TV-band device {{Short description, Radio frequency device
TV band devices or TVBDs are unlicensed radio frequency devices operating in the vacant channels or white spaces between US television channels in the range of 54 to 698 MHz. The rules defining these ...
s. Other countries have similar band limits; for example, Great Britain's UHF TV band currently (Jan 2014) extends from 470 MHz to 790 MHz. Typically, wireless microphones operate on unused TV channels (" white spaces"), with room for one to two microphones per megahertz of spectrum available. (" Wo Mic")
Intermodulation (IM) is a major problem when operating multiple systems in one location. IM occurs when two or more RF signals mix in a non-linear circuit, such as an oscillator or mixer. When this occurs, predictable combinations of these frequencies can occur. For example, the combinations 2A-B, 2B-A, and A+B-C might occur, where A, B, and C are the frequencies in operation. If one of these combinations is close to the operating frequency of another system (or one of the original frequencies A, B, or C), then interference will result on that channel. The solution to this problem is to manually calculate all of the possible products, or use a computer program that does this calculation automatically.
Digital Hybrid Wireless
Digital Hybrid systems use an analogue FM transmission scheme in combination with digital signal processing (DSP) to enhance the system's audio. Using DSP allows the use of digital techniques impossible in the analogue domain such as predictive algorithms, thus achieving a flatter frequency response in the audio spectrum and also further reducing noise and other undesirable artifacts when compared to pure analogue systems.
Another approach is to use DSP in order to emulate analogue companding schemes in order to maintain compatibility between older analogue systems and newer systems. Using DSP in the receiver alone can improve the overall audio performance without the penalty of increased energy consumption and resulting battery life reduction that is incurred by incorporating DSP into a battery-powered transmitter.
Digital
A number of pure digital wireless microphone systems do exist, and there are many different digital modulation schemes possible.
Digital systems from Sennheiser, Sony, Shure, Zaxcom, AKG and MIPRO use the same UHF frequencies used by analogue FM systems for transmission of a digital signal at a fixed bit rate. These systems encode an RF carrier with one channel, or in some cases two channels, of digital audio. Only the Sennheiser Digital 9000 system, introduced in 2013, is currently capable of transmitting full-bandwidth, uncompressed, digital audio in the same 200 kHz bandwidth UHF channels that were used by analogue FM systems. The advantages offered by purely digital systems include low noise, low distortion, the opportunity for encryption, and enhanced transmission reliability.
Pure digital systems take various forms. Some systems use frequency-hopping spread spectrum
Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly changing the carrier frequency among many distinct frequencies occupying a large spectral band. The changes are controlled by a code known to both tr ...
technology, similar to that used for cordless phones and radio-controlled models. As this can require more bandwidth than a wideband FM signal, these microphones typically operate in the unlicensed 900 MHz, 2.4 GHz or 6 GHz bands. The absence of any requirement for a license in these frequency bands is an added attraction for many users, regardless of the technology used. The 900 MHz band is not an option outside of the US and Canada as it is used by GSM cellular mobile phone networks in most other parts of the world. The 2.4 GHz band is increasingly congested with various systems including WiFi (also referred to as Wireless LAN, wireless networks, 802.11b/g/n), Bluetooth and 'leakage' from microwave ovens. The 6 GHz band has problems of range (requires line of sight) due to the extremely short transmission carrier wavelengths. The Alteros GTX Series is a local area wireless microphone network that overcomes the line-of-sight problem by utilizing up to 64 transceivers around the performance area. It is also the only system employing Ultra WideBand pulsed RF technology which doesn't generate intermodulation products common with FM, QAM and GFSK modulated carriers used by most other systems.
Digital radio microphones are inherently more difficult for the casual ' scanner' listener to intercept because conventional "scanning receivers" are generally only capable of de-modulating conventional analogue modulation schemes such as FM and AM. However, some digital wireless microphone systems additionally offer encryption
In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decip ...
technology in an attempt to prevent more serious 'eavesdropping' which may be of concern for corporate users and those using radio microphones in security sensitive situations.
Manufacturers currently offering digital wireless microphone systems include AKG-Acoustics, Alteros, Audio-Technica, Lectrosonics, Line 6, MIPRO, Shure
Shure Incorporated is an American audio products corporation. It was founded by Sidney N. Shure in Chicago, Illinois, in 1925 as a supplier of radio parts kits. The company became a consumer and professional audio-electronics manufacturer of mi ...
, Sony, Sennheiser and Zaxcom. All are using different digital modulation schemes from each other.
Licensing
United Kingdom
In the UK, use of wireless microphone systems requires a Wireless Telegraphy Act license, except for the license free bands of 173.8–175.0 MHz and 863–865 MHz. In 2013 the UK communications regulator, Ofcom
The Office of Communications, commonly known as Ofcom, is the government-approved regulatory and competition authority for the broadcasting, telecommunications and postal industries of the United Kingdom.
Ofcom has wide-ranging powers acros ...
, held an auction in which the UHF band from 790 MHz to 862 MHz was sold to be used for mobile broadband services.
United States
Licenses are required to use wireless microphones on vacant TV channels in the United States as they are a part of the Broadcast Auxiliary Service (BAS). Licenses are available only to broadcasters, cable networks, television and film producers.
There are currently some wireless microphone manufacturers that are marketing wireless microphones for use in the United States that operate within the 944–952 MHz band reserved for studio-transmitter link
A studio transmitter link (or STL) sends a radio station's or television station's audio and video from the broadcast studio or origination facility to a radio transmitter, television transmitter or uplink facility in another location. This is ...
communications. Beginning in 2017, the amount of TV band spectrum available for wireless microphone use is decreasing as a result of the incentive auction, which was completed on April 13, 2017.
Australia
In Australia, operation of wireless microphones of up to 100 mW EIRP between 520 MHz and 694 MHz is on unused television channels and is covered by a class license, allowing any user to operate the devices without obtaining an individual license.
Other countries
In many other countries wireless microphone use does require a license. Some governments regard all radio frequencies as military assets and the use of unlicensed radio transmitters, even wireless microphones, may be severely punished.
Licensing in European countries is regulated by the Electronic Communications Committee (ECC) which is part of the (CEPT) based in Denmark.
White Space Devices (United States)
There is a move to allow the operation of personal unlicensed wideband digital devices using the UHF television spectrum in the United States. These ' white space' devices (WSDs) would be required to have GPS
The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...
and access to a location database to avoid interfering with other users of the band. Initial tests performed by the FCC showed that, in some cases, prototypes of these devices were unable to correctly identify frequencies that were in use, and might therefore accidentally transmit on top of these users. Broadcasters, theaters, and wireless microphone manufacturers were firmly against these types of devices ostensibly for this reason.
Later tests by the FCC indicated that the devices could safely be used. This did not reduce the opposition by broadcasters who might also have been concerned by the possibility of entertainment delivery competition from high-speed mobile Internet access delivered in the white spaces.
On September 23, 2010, the FCC released a Memorandum Opinion and Order that determined the final rules for the use of white space for unlicensed wireless devices. The final rules adopt a proposal from the White Spaces Coalition for very strict emission rules that prevent the direct use of IEEE 802.11 (Wi-Fi) in a single channel effectively making the new spectrum unusable for Wi-Fi technologies.
Cognitive Access (UK)
A similar class of device to those known in the US as White Space Devices (WSD) is being researched in the UK and probably many other countries. Whilst the WSD situation in the US is being closely watched by interested parties in the UK and elsewhere, early in 2009 Ofcom launched research and a public consultation on Cognitive Access to the UHF interleaved spectrum. The outcome of this consultation and the related WSD activities in the US could have far reaching implications for users of UHF radio microphones in the UK and around the world.
See also
*Boom operator (media)
A boom operator (or First Assistant Sound) is a core role in the sound department of a film production, who works with the production sound mixer and utility sound technician. The principal responsibility of the boom operator is microphone ...
*Electronic field production
Electronic field production (EFP) is a television industry term referring to a video production which takes place in the field, outside of a formal television studio, in a practical location or special venue. ZettlHerbert Zettl, ''Television Pro ...
(EFP)
*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 ...
(ENG)
*Filmmaking
Filmmaking (film production) is the process by which a motion picture is produced. Filmmaking involves a number of complex and discrete stages, starting with an initial story, idea, or commission. It then continues through screenwriting, casti ...
*FM transmitter (personal device)
A personal FM transmitter is a low-power FM radio transmitter that broadcasts a signal from a portable audio device (such as an MP3 player) to a standard FM radio. Most of these transmitters plug into the device's headphone jack and then broadca ...
*Professional video camera
A professional video camera (often called a television camera even though its use has spread beyond television) is a high-end device for creating electronic moving images (as opposed to a movie camera, that earlier recorded the images on film). O ...
*Recording studio
A recording studio is a specialized facility for sound recording, mixing, and audio production of instrumental or vocal musical performances, spoken words, and other sounds. They range in size from a small in-home project studio large enoug ...
*Television production
A television show – or simply TV show – is any content produced for viewing on a television set which can be broadcast via over-the-air, satellite, or cable, excluding breaking news, advertisements, or trailers that are typically placed betw ...
References
External links
Discussion regarding the reassignment of Channel 69 frequencies in the UK
{{DEFAULTSORT:Wireless Microphone
Microphones
Wireless transmitters
fi:Langaton mikrofoni