1080p is a set of HDTV high-definition video modes characterized by 1,920 pixels displayed across the screen horizontally and 1,080 pixels down the screen vertically. The term assumes a widescreen aspect ratio of 16:9, implying a resolution of 2.1 megapixels. It is marketed as full HD, to contrast 1080p with 720p resolution screens. 1080p video signals are supported by ATSC standards in the United States and DVB standards in Europe. Applications of the 1080p standard include television broadcasts, Blu-ray Discs, Internet content such as YouTube videos and Netflix TV shows and movies, consumer-grade televisions and projectors, computer monitors and video game consoles. Small camcorders and digital cameras can capture still and moving images in 1080p resolution. Any screen device that advertises 1080p refers to the ability to accept 1080p signals in native resolution format, which means there are a true 1920 pixels in width and 1080 pixels in height, the display is not over-scanning, under-scanning, or reinterpreting the signal to a lower resolution.
The HD ready 1080p logo program, by DIGITALEUROPE, requires that certified TV sets support 1080p 24 fps, 1080p 50 fps, 1080p 60 fps formats, among other requirements, with fps meaning frames per second. For live broadcast applications, a high-definition progressive scan format operating at 1080p at 50 or 60 frames per second is being evaluated as a future standard for moving picture acquisition. Although 24 frames per second is used for shooting the movies. EBU has been endorsing 1080p50 as a future-proof production format because it improves resolution and requires no deinterlacing, allows broadcasting of standard 1080i25 and 720p50 signal alongside 1080p50 in the current infrastructure and is compatible with DCI distribution formats.1080p50/p60 production format requires a whole new range of studio equipment including cameras and editing systems, contribution links as it has doubled the data rate of current 50 or 60 fields interlaced 1920x1080 from 1.485 Gbit/s to nominally 3 Gbit/s using uncompressed RGB encoding.
Most current revisions of SMPTE 372M, SMPTE 424M and EBU Tech 3299 require YCbCr color space and 4:2:2 chroma subsampling for transmitting 1080p50 and 1080p60 signal. Studies from 2009 show that for digital broadcasts compressed with H.264/AVC, transmission bandwidth savings of interlaced video over progressive video are minimal when using twice the frame rate. In the United States, the original ATSC standards for HDTV supported 1080p video, but only at the frame rates of 23.976, 24, 25, 29.97 and 30 frames per second. In July 2008, the ATSC standards were amended to include H.264/MPEG-4 AVC compression and 1080p at 50, 59.94 and 60 frames per second. Such frame rates require H.264/AVC High Profile Level 4.2, while standard HDTV frame rates only require Level 4.0. This update is not expected to result in widespread availability of 1080p60 programming, since most of the existing digital receivers in use would only be able to decode the older, less-efficient MPEG-2 codec, because there is a limited amount of bandwidth for subchannels.
In Europe, 1080p25 signals have been supported by the DVB suite of broadcasting standards. The 1080p50 format is considered to be a future-proof production format and a future broadcasting format. 1080p50 broadcasting should require the same bandwidth as 1080i50 signal and only 15–20% more than that of 720p50 signal due to increased compression efficiency, though 1080p50 production requires more bandwidth or more efficient codecs such as JPEG 2000, high-bitrate MPEG-2, or H.264/AVC and HEVC. In September 2009, ETSI and EBU, the maintainers of the DVB suite, added support for 1080p50 signal coded with MPEG-4 AVC High Profile Level 4.2 with Scalable Video Coding extensions or VC-1 Advanced Profile compression. EBU requires that legacy MPEG-4 AVC decoders should avoid crashing in the presence of SVC or 1080p50 packets. SVC enables forward compatibility with 1080p50 and 1080p60 broadcasting for older MPEG-4 AVC receivers, so they will only recognize baseline SVC stream coded at a lower resolution or frame rate and will gracefully ignore additional packets, while newer hardware will be able to decode full-resolution signal.
In June 2016, EBU announced the "Advanced 1080p" format which will include UHD Phase A features such as high-dynamic-range video at 10 and 12 bit color and BT.2020 color gamut, optional HFR 100, 120/1.001 and 120 Hz. The ITU-T BT.2100 standard that includes Advanced 1080p video was subsequently published in July 2016. In practice, 1080p refers to a 1920×1080 raster with a 16:9 picture aspect ratio and a 1:1 pixel aspect ratio; the following is a list other resolutions with a picture height of 1080 lines that are sometimes used in practice. In the United States, 1080p over-the-air are being broadcast experimentally using ATSC 3.0 on NBC Affiliate WRAL-TV in North Carolina, with select stations in the US announcing that there will be new ATSC 3.0 technology that will be transmitted with 1080p Broadcast television, such as Fox Affiliate WJW-TV in Cleveland
Sri Lanka the Democratic Socialist Republic of Sri Lanka, is an island country in South Asia, located in the Indian Ocean to the southwest of the Bay of Bengal and to the southeast of the Arabian Sea. The island is geographically separated from the Indian subcontinent by the Gulf of Mannar and the Palk Strait; the legislative capital, Sri Jayawardenepura Kotte, is a suburb of the commercial capital and largest city, Colombo. Sri Lanka's documented history spans 3,000 years, with evidence of pre-historic human settlements dating back to at least 125,000 years, it has a rich cultural heritage and the first known Buddhist writings of Sri Lanka, the Pāli Canon, date back to the Fourth Buddhist council in 29 BC. Its geographic location and deep harbours made it of great strategic importance from the time of the ancient Silk Road through to the modern Maritime Silk Road. Sri Lanka was known from the beginning of British colonial rule as Ceylon. A nationalist political movement arose in the country in the early 20th century to obtain political independence, granted in 1948.
Sri Lanka's recent history has been marred by a 26-year civil war, which decisively ended when the Sri Lanka Armed Forces defeated the Liberation Tigers of Tamil Eelam in 2009. The current constitution stipulates the political system as a republic and a unitary state governed by a semi-presidential system, it has had a long history of international engagement, as a founding member of the South Asian Association for Regional Cooperation, a member of the United Nations, the Commonwealth of Nations, the G77, the Non-Aligned Movement. Along with the Maldives, Sri Lanka is one of only two South Asian countries rated "high" on the Human Development Index, with its HDI rating and per capita income the highest among South Asian nations; the Sri Lankan constitution accords Buddhism the "foremost place", although it does not identify it as a state religion. Buddhism is given special privileges in the Sri Lankan constitution; the island is home to many cultures and ethnicities. The majority of the population is from the Sinhalese ethnicity, while a large minority of Tamils have played an influential role in the island's history.
Moors, Malays and the indigenous Vedda are established groups on the island. In antiquity, Sri Lanka was known to travellers by a variety of names. According to the Mahavamsa, the legendary Prince Vijaya named the land Tambapanni, because his followers' hands were reddened by the red soil of the area. In Hindu mythology, such as the Ramayana, the island was referred to as Lankā; the Tamil term Eelam, was used to designate the whole island in Sangam literature. The island was known under Chola rule as Mummudi Cholamandalam. Ancient Greek geographers called it Taprobanē from the word Tambapanni; the Persians and Arabs referred to it as Sarandīb from Cerentivu or Siṃhaladvīpaḥ. Ceilão, the name given to Sri Lanka by the Portuguese Empire when it arrived in 1505, was transliterated into English as Ceylon; as a British crown colony, the island was known as Ceylon. The country is now known in Sinhala in Tamil as Ilaṅkai. In 1972, its formal name was changed to "Free and Independent Republic of Sri Lanka".
In 1978 it was changed to the "Democratic Socialist Republic of Sri Lanka". As the name Ceylon still appears in the names of a number of organisations, the Sri Lankan government announced in 2011 a plan to rename all those over which it has authority; the pre-history of Sri Lanka goes back 125,000 years and even as far back as 500,000 years. The era spans the Palaeolithic and early Iron Ages. Among the Paleolithic human settlements discovered in Sri Lanka, which dates back to 37,000 BP, Batadombalena and Belilena are the most important. In these caves, archaeologists have found the remains of anatomically modern humans which they have named Balangoda Man, other evidence suggesting that they may have engaged in agriculture and kept domestic dogs for driving game. One of the first written references to the island is found in the Indian epic Ramayana, which provides details of a kingdom named Lanka, created by the divine sculptor Vishwakarma for Kubera, the Lord of Wealth, it is said that Kubera was overthrown by his demon stepbrother Ravana, the powerful emperor who built a mythical flying machine named Dandu Monara.
The modern city of Wariyapola is described as Ravana's airport. Early inhabitants of Sri Lanka were ancestors of the Vedda people, an indigenous people numbering 2,500 living in modern-day Sri Lanka; the 19th-century Irish historian James Emerson Tennent theorized that Galle, a city in southern Sri Lanka, was the ancient seaport of Tarshish from which King Solomon is said to have drawn ivory and other valuables. According to the Mahāvamsa, a chronicle written in Pāḷi, the original inhabitants of Sri Lanka are the Yakshas and Nagas. Ancient cemeteries that were used before 600 BC and other signs of advanced civilisation have been discovered in Sri Lanka. Sinhalese history traditionally starts in 543 BC with the arrival of Prince Vijaya, a semi-legendary prince who sailed with 700 followers to Sri Lanka, after being expelled from Vanga Kingdom (present-day Ben
Colombo is the commercial capital and largest city of Sri Lanka by population. According to the Brookings Institution, Colombo metropolitan area has a population of 5.6 million, 752,993 in the city proper. It is the financial centre of a popular tourist destination, it is located on the west coast of the island and adjacent to the Greater Colombo area which includes Sri Jayawardenepura Kotte, the legislative capital of Sri Lanka and Dehiwala-Mount Lavinia. Colombo is referred to as the capital since Sri Jayawardenepura Kotte is within the urban area of, a suburb of, Colombo, it is the administrative capital of the Western Province and the district capital of Colombo District. Colombo is a vibrant place with a mixture of modern life and colonial buildings and ruins, it was the legislative capital of Sri Lanka until 1982. Due to its large harbour and its strategic position along the East-West sea trade routes, Colombo was known to ancient traders 2,000 years ago, it was made the capital of the island when Sri Lanka was ceded to the British Empire in 1815, its status as capital was retained when the nation became independent in 1948.
In 1978, when administrative functions were moved to Sri Jayawardenepura Kotte, Colombo was designated as the commercial capital of Sri Lanka. Like many cities, Colombo's urban area extends well beyond the boundaries of a single local authority, encompassing other municipal and urban councils such as Sri Jayawardenepura Kotte Municipal Council, Dehiwala Mount Lavinia Municipal Council, Kolonnawa Urban Council, Kaduwela Municipal Council and Kotikawatte Mulleriyawa Pradeshiya Sabha; the main city is home to a majority of Sri Lanka's corporate offices and entertainment venues. Famous landmarks in Colombo include Galle Face Green, Viharamahadevi Park, Beira Lake, Colombo Racecourse, University of Colombo, Mount Lavinia beach, Nelum Pokuna Theatre, Colombo Lotus Tower as well as the National Museum; the name "Colombo", first introduced by the Portuguese in 1505, is believed to be derived from the classical Sinhala name කොලොන් තොට Kolon thota, meaning "port on the river Kelani". Another belief is that the name is derived from the Sinhala name කොල-අඹ-තොට Kola-amba-thota which means "Harbour with leafy mango trees".
This coincides with Robert Knox's history of the island. He writes that, "On the West the City of Columbo, so called from a Tree the Natives call Ambo, growing in that place; the author of the oldest Sinhala grammar, written in the 13th century wrote about a category of words that belonged to early Sinhala. It lists kolamba as belonging to an indigenous source. Kolamba may be the source of the name of the commercial capital Colombo; as Colombo possesses a natural harbour, it was known to Indian, Persian, Roman and Chinese traders over 2,000 years ago. Traveller Ibn Battuta who visited the island in the 14th century, referred to it as Kalanpu. Arabs, whose prime interests were trade, began to settle in Colombo around the 8th century AD because the port helped their business by the way of controlling much of the trade between the Sinhalese kingdoms and the outside world, their descendants now comprise the local Sri Lankan Moor community. Portuguese explorers led by Dom Lourenço de Almeida first arrived in Sri Lanka in 1505.
During their initial visit they made a treaty with the King of Kotte, Parakramabahu VIII, which enabled them to trade in the island's crop of cinnamon, which lay along the coastal areas of the island, including in Colombo. As part of the treaty, the Portuguese were given full authority over the coastline in exchange for the promise of guarding the coast against invaders, they were allowed to establish a trading post in Colombo. Within a short time, they expelled the Muslim inhabitants of Colombo and began to build a fort in 1517; the Portuguese soon realized that control of Sri Lanka was necessary for protection of their coastal establishments in India and they began to manipulate the rulers of the Kotte kingdom to gain control of the area. After skilfully exploiting rivalries within the royal family, they took control of a large area of the kingdom and the Sinhalese King Mayadunne established a new kingdom at Sitawaka, a domain in the Kotte kingdom. Before long he annexed much of the Kotte kingdom and forced the Portuguese to retreat to Colombo, besieged by Mayadunne and the kings of Sitawaka, forcing them to seek reinforcement from their major base in Goa, India.
Following the fall of the kingdom in 1593, the Portuguese were able to establish complete control over the coastal area, with Colombo as their capital. This part of Colombo is still known as Fort and houses the presidential palace and the majority of Colombo's five star hotels; the area outside Fort is known as Pettah and is a commercial hub. In 1638 the Dutch signed a treaty with King Rajasinha II of Kandy which assured the king assistance in his war against the Portuguese in exchange for a monopoly of the island's major trade goods; the Portuguese resisted the Dutch and the Kandyans but were defeated in their strongholds beginning in 1639. The Dutch captured Colombo in 1656 after an epic siege, at the end of which a mere 93 Portuguese survivors were given safe conduct out of the fort. Although the Dutch
Battaramulla is a suburb of the city of Colombo, situated 5.2 miles from the City Centre at Colombo Fort, near the Parliament of Sri Lanka. It is one of the fastest developing administrative and residential areas in the Colombo District being home to the country's elite. By present Battaramulla has been an important town in Sri Lanka, because of the Sri Lanka government decided to locate all the government department head offices in this town. Battaramulla has always been an adjunct to Kotte, which lay on the opposite side of the Diyawanna Oya. At the time of the Kotte Kingdom, the cooks at the royal palace would travel there daily by ferry across the Diyawanna Oya; the place they embarked was called bat-tota-mulla, which became'Battaramulla'. Kotiyagoda, a suburb of Battaramulla, derived its name from kotuwe-egoda; this pattern was followed when the Parliament was shifted to the Doowa island in Kotte, several government offices being set up in Battaramulla thereafter. After the British invasion of the island, they built a Church in 1850 in Battaramulla, but after that they called the village Thalangama.
The invaders wanted to eliminate the name of the old village Battaramulla and mentioned the area as Thalangama in every legal document. However the old Sinhala Buddhist villages wanted to protect the old village name Battaramulla. In 1887 a temple called Sri Sudharmaramaya was established in Battaramulla and the buddhist monks in the temple emphasized the importance of protecting old name of the village which belonged to the Kotte kingdom earlier. After establishing postal service in Sri Lanka the post office established in Battaramulla, called as Thalangama sub post office; however after getting the independence, in 1970 this mistake was re-corrected by promoting the sub post office into a main post office called as Battaramulla. The Battaramulla, Pelawatte and Kalapaluwawa areas, which comprise Battaramulla was governed by a separate municipal structure called the Battaramulla Town Council, it was dissolved and the area is now administered by the Kaduwela Municipal Council. The Battaramulla District Office of Kaduwela municipal council is the administrative office of the area, located at Pannipitiya road.
In Sri Lanka an area is identified by the name of the main post office. In that way Battaramulla main post office belongs the following villages mainly. Battaramulla Junction, Battaramulla South, Battaramulla North, Koswatta, Jayanthipura, Polduwa, Udumulla, Thalangama North, Thalangama South, Nagahamulla, Wickramasinghapura, Akuregoda, Korambe, Aruppitiya; the Thalawathugoda, Sri Jayawardenapura-Kotte and Malabe suburbs mark the borders of Battaramulla. There are number of public bus services available to reach Battaramulla town from Colombo City. Route number 171 is the main public bus service, started from Colombo-Fort and ended at Kandawatta Junction. Route number 152 buses come to Denzil kobbekaduwa Mawatha via Mulleriawa side. Additionally you can reach to Battaramulla town by route no 170 - Athurugiriya, route no 190 - Meegoda, route no 174 Kottawa, route no 186 - Jayawadanagama and route no 177 - Kaduwela buses from the Colombo city. From Dehiwala town, located on the Colombo - Galle main road you can take route no 163 buses to reach to Battaramulla.
These buses come via Kotte. From Kandy city or Kurunegala town you can take route no 17 - Panadura buses; these buses come more than 100 km from Kandy and Kurunegala via main towns like Peradeniya, Mawanella, Polgahawela, Warakapola and Kaduwela. If you come from Panadura side, you can reach to Battaramulla by route no 17 - Kandy or Kurunegala buses and they come via Moratuwa, Galkissa, Dehiwala and Kotte. A government bus runs inside the town area under route no 374 which starts from Battaramulla main junction and ends at Pelawatta junction via Ganahena, Robert Gunawardhana Mawatha, Korambe and Akuregoda. In addition to the public bus services there are office time bus services which arrive to Battaramulla town, in the morning and depart from the town in the evening only in government office working days. Buses that pass through Battaramulla are Kottawa - Borella, Battaramulla - Dehiwala, Koswatta/Pelawatta - Fort, Athurugiriya - Pettah Meegoda - Pettah A notable expatriate population and affluent nationals of Sri Lanka live in Battaramulla.
The rapid increase in the elite and affluent moving into the area has contributed to the economic boom in the area. The population of Battaramulla is 75633 according to the GeoNames geographical database. Majority is Sinhalese. By early 80's there were many traditional villagers in the area, but the rapid increase of the land value in the area has followed with them selling off and moving to areas further from Colombo; the Oldest International school in Sri Lanka, catering to the expatriate community and a few select nationals. Sri Subhuthi Central College, located at Robert Gunawardhana Mawatha is the main government school in the area. There are number of government schools located in the area like Lanka Sabaha Junior School, Indrajothi Vidyalaya, M. D. H. Jayawardhana Vidyala
Color television is a television transmission technology that includes information on the color of the picture, so the video image can be displayed in color on the television set. It is an improvement on the earliest television technology, monochrome or black and white television, in which the image is displayed in shades of gray. Television broadcasting stations and networks in most parts of the world upgraded from black and white to color transmission in the 1970s and 1980s; the invention of color television standards is an important part of the history of television, it is described in the technology of television article. Transmission of color images using mechanical scanners had been conceived as early as the 1880s. A practical demonstration of mechanically-scanned color television was given by John Logie Baird in 1928, but the limitations of a mechanical system were apparent then. Development of electronic scanning and display made an all-electronic system possible. Early monochrome transmission standards were developed prior to the Second World War, but civilian electronics developments were frozen during much of the war.
In August 1944, Baird gave the world's first demonstration of a practical electronic color television display. In the United States, commercially competing color standards were developed resulting in the NTSC standard for color that retained compatibility with the prior monochrome system. Although the NTSC color standard was proclaimed in 1953 and limited programming became available, it was not until the early 1970s that color television in North America outsold black and white or monochrome units. Color broadcasting in Europe was not standardized on the SECAM formats until the 1960s. Broadcasters began to switch from analog color television technology to digital television around 2006; this changeover is now complete in many countries, but analog television is still the standard elsewhere. The human eye's detection system, in the retina, consists of two types of light detectors: rod cells that capture light and shapes/figures, the cone cells that detect color. A typical retina contains 120 million rods and 4.5 million to 6 million cones, which are divided among three groups that are sensitive to red and blue light.
This means that the eye has far more resolution in "luminance", than in color. However, post-processing of the optic nerve and other portions of the human visual system combine the information from the rods and cones to re-create what appears to be a high-resolution color image; the eye has limited bandwidth to the rest of the visual system, estimated at just under 8 Mbit/s. This manifests itself in a number of ways, but the most important in terms of producing moving images is the way that a series of still images displayed in quick succession will appear to be continuous smooth motion; this illusion starts to work at about 16 frame/s, common motion pictures use 24 frame/s. Television, using power from the electrical grid, tunes its rate in order to avoid interference with the alternating current being supplied – in North America, some Central and South American countries, Korea, part of Japan, the Philippines, a few other countries, this is 60 video fields per second to match the 60 Hz power, while in most other countries it is 50 fields per second to match the 50 Hz power.
In its most basic form, a color broadcast can be created by broadcasting three monochrome images, one each in the three colors of red and blue. When displayed together or in rapid succession, these images will blend together to produce a full-color image as seen by the viewer. One of the great technical challenges of introducing color broadcast television was the desire to conserve bandwidth three times that of the existing black-and-white standards, not use an excessive amount of radio spectrum. In the United States, after considerable research, the National Television Systems Committee approved an all-electronic system developed by RCA which encoded the color information separately from the brightness information and reduced the resolution of the color information in order to conserve bandwidth; the brightness image remained compatible with existing black-and-white television sets at reduced resolution, while color televisions could decode the extra information in the signal and produce a limited-resolution color display.
The higher resolution black-and-white and lower resolution color images combine in the eye to produce a high-resolution color image. The NTSC standard represented a major technical achievement. Experiments in television systems using radio broadcasts date to the 19th century, but it was not until the 20th century that advances in electronics and light detectors made development practical. A key problem was the need to convert a 2D image into a "1D" radio signal. Early systems used a device known as a "Nipkow disk", a spinning disk with a series of holes punched in it that caused a spot to scan across and down the image. A single photodetector behind the disk captured the image brightness at any given spot, converted into a radio signal and broadcast. A similar disk was used at the receiver side, with a light source behind the disk instead of a detector. A number of such systems were being used experimentally in the 1920s; the best-known was John Logie Baird's, used for regular public broadcasting in Britain for several years.
Indeed, Baird's system was demonstrated to members of the Royal Institution in London in 1926 in what is recognized as the first demonstration of a true, working television system. In spite of these early successes, all mechanical television systems sh
FM broadcasting is a method of radio broadcasting using frequency modulation technology. Invented in 1933 by American engineer Edwin Armstrong, wide-band FM is used worldwide to provide high-fidelity sound over broadcast radio. FM broadcasting is capable of better sound quality than AM broadcasting, the chief competing radio broadcasting technology, so it is used for most music broadcasts. Theoretically wideband AM can offer good sound quality, provided the reception conditions are ideal. FM radio stations use the VHF frequencies; the term "FM band" describes the frequency band in a given country, dedicated to FM broadcasting. Throughout the world, the FM broadcast band falls within the VHF part of the radio spectrum. 87.5 to 108.0 MHz is used, or some portion thereof, with few exceptions: In the former Soviet republics, some former Eastern Bloc countries, the older 65.8–74 MHz band is used. Assigned frequencies are at intervals of 30 kHz; this band, sometimes referred to as the OIRT band, is being phased out in many countries.
In those countries the 87.5–108.0 MHz band is referred to as the CCIR band. In Japan, the band 76–95 MHz is used; the frequency of an FM broadcast station is an exact multiple of 100 kHz. In most of South Korea, the Americas, the Philippines and the Caribbean, only odd multiples are used. In some parts of Europe and Africa, only multiples are used. In the UK odd or are used. In Italy, multiples of 50 kHz are used. In most countries the maximum permitted frequency error is specified, the unmodulated carrier should be within 2000 Hz of the assigned frequency. There are other unusual and obsolete FM broadcasting standards in some countries, including 1, 10, 30, 74, 500, 300 kHz. However, to minimise inter-channel interference, stations operating from the same or geographically close transmitter sites tend to keep to at least a 500 kHz frequency separation when closer frequency spacing is technically permitted, with closer tunings reserved for more distantly spaced transmitters, as interfering signals are more attenuated and so have less effect on neighboring frequencies.
Frequency modulation or FM is a form of modulation which conveys information by varying the frequency of a carrier wave. With FM, frequency deviation from the assigned carrier frequency at any instant is directly proportional to the amplitude of the input signal, determining the instantaneous frequency of the transmitted signal; because transmitted FM signals use more bandwidth than AM signals, this form of modulation is used with the higher frequencies used by TV, the FM broadcast band, land mobile radio systems. The maximum frequency deviation of the carrier is specified and regulated by the licensing authorities in each country. For a stereo broadcast, the maximum permitted carrier deviation is invariably ±75 kHz, although a little higher is permitted in the United States when SCA systems are used. For a monophonic broadcast, again the most common permitted. However, some countries specify a lower value for monophonic broadcasts, such as ±50 kHz. Random noise has a triangular spectral distribution in an FM system, with the effect that noise occurs predominantly at the highest audio frequencies within the baseband.
This can be offset, to a limited extent, by boosting the high frequencies before transmission and reducing them by a corresponding amount in the receiver. Reducing the high audio frequencies in the receiver reduces the high-frequency noise; these processes of boosting and reducing certain frequencies are known as pre-emphasis and de-emphasis, respectively. The amount of pre-emphasis and de-emphasis used is defined by the time constant of a simple RC filter circuit. In most of the world a 50 µs time constant is used. In the Americas and South Korea, 75 µs is used; this applies to both stereo transmissions. For stereo, pre-emphasis is applied to the left and right channels before multiplexing; the use of pre-emphasis becomes a problem because of the fact that many forms of contemporary music contain more high-frequency energy than the musical styles which prevailed at the birth of FM broadcasting. Pre-emphasizing these high frequency sounds would cause excessive deviation of the FM carrier. Modulation control devices are used to prevent this.
Systems more modern than FM broadcasting tend to use either programme-dependent variable pre-emphasis. Long before FM stereo transmission was considered, FM multiplexing of other types of audio level information was experimented with. Edwin Armstrong who invented FM was the first to experiment with multiplexing, at his experimental 41 MHz station W2XDG located on the 85th floor of the Empire State Building in New York City; these FM multiplex transmissions started in November 1934 and consisted of the main channel audio program and three subcarriers: a fax program, a synchronizing signal for the fax program and a telegraph “order” channel. These original FM multiplex subcarriers were amplitude modulated. Two musical programs, consisting of both the Red and Blue Network program feeds of the NBC Radio Network, were transmitted using the same system of subcarrier modulation as part of a studio-to-transmitter link system. In April 1935, the AM subcarriers were replaced with much improved results.
The first FM subcarrier transmissions emanating from Major Armstrong's experimental station KE2XCC at Alpine, New Jersey occurred in 1948. These transmissions consisted of two-cha