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Near Instantaneous Companded Audio Multiplex (NICAM) is an early form of
lossy compression In information technology, lossy compression or irreversible compression is the class of data compression methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data si ...
for
digital audio Digital audio is a representation of sound recorded in, or converted into, digital form. In digital audio, the sound wave of the audio signal is typically encoded as numerical samples in a continuous sequence. For example, in CD audio, samp ...
. It was originally developed in the early 1970s for point-to-point links within broadcasting networks.Croll, M.G., Osborne, D.W. and Spicer, C.R. (1974), ''Digital sound signals: the present BBC distribution system and a proposal for bit-rate reduction by digital companding''. IEE Conference publication No. 119, pp. 90–96 In the 1980s, broadcasters began to use NICAM compression for transmissions of
stereo Stereophonic sound, or more commonly stereo, is a method of sound reproduction that recreates a multi-directional, 3-dimensional audible perspective. This is usually achieved by using two independent audio channels through a configuration ...
TV sound to the public.


History


Near-instantaneous companding

The idea was first described in 1964. In this, the 'ranging' was to be applied to the analogue signal before the analogue-to-digital converter (ADC) and after the digital-to-analogue converter (DAC). The application of this to broadcasting, in which the
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 expandi ...
was to be done entirely digitally after the ADC and before the DAC, was described in a 1972
BBC Research BBC Research & Development is the technical research department of the BBC. Function It has responsibility for researching and developing advanced and emerging media technologies for the benefit of the corporation, and wider UK and European m ...
Report.


Point-to-point links

NICAM was originally intended to provide broadcasters with six high-quality audio channels within a total bandwidth of 2048 kbit/s. This figure was chosen to match the E1 primary
multiplex Multiplex may refer to: * Multiplex (automobile), a former American car make * Multiplex (comics), a DC comic book supervillain * Multiplex (company), a global contracting and development company * Multiplex (assay), a biological assay which measu ...
rate, and systems using this rate could make use of the planned PDH national and international telecommunications networks. Several similar systems had been developed in various countries, and in about 1977/78 the BBC Research Department conducted listening tests to evaluate them. The candidates were: * A RAI system which used
A-law An A-law algorithm is a standard companding algorithm, used in European 8-bit PCM digital communications systems to optimize, i.e. modify, the dynamic range of an analog signal for digitizing. It is one of two versions of the G.711 standar ...
companding to compress 14-bit
linear PCM Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the am ...
samples into 10 bits (14:10) * A NICAM-type system proposed by
Télédiffusion de France TDF (which stands for ''Télédiffusion de France'' officially renamed ''TDF'' in 2004) is a French company which provides radio and television transmission services, services for telecommunications operators, and other multimedia services � ...
(14:9) * NICAM-1 (13:10) * NICAM-2 (14:11) * NICAM-3 (14:10) It was found that NICAM-2 provided the best sound quality, but reduced programme-modulated noise to an unnecessarily low level at the expense of bit rate. NICAM-3, which had been proposed during the test to address this, was selected as the winner.Jones, A.H. (1978), ''Digital coding of audio signals for point-to-point transmission''. IEE Conference Publication No. 166, pp. 25–28 Audio is encoded using 14 bit
pulse-code modulation Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the ...
at a sampling rate of 32 kHz.


Broadcasts to the public

NICAM's second role – transmission to the public – was developed in the 80s by the BBC. This variant was known as NICAM-728, after the 728 kbit/s
bitstream A bitstream (or bit stream), also known as binary sequence, is a sequence of bits. A bytestream is a sequence of bytes. Typically, each byte is an 8-bit quantity, and so the term octet stream is sometimes used interchangeably. An octet may ...
it is sent over. It uses the same audio coding parameters as NICAM-3. The first NICAM digital
stereo Stereophonic sound, or more commonly stereo, is a method of sound reproduction that recreates a multi-directional, 3-dimensional audible perspective. This is usually achieved by using two independent audio channels through a configuration ...
programme was the First Night of the 92nd edition of the Proms which was broadcast on BBC2 from the Crystal Palace transmitting station in London on 18 July 1986, though programmes were not advertised as being broadcast in stereo on the BBC until some five years later, when the majority of the country's transmitters had been upgraded to broadcast NICAM, and a large number of BBC programmes were being made in stereo. The BBC publicly launched their NICAM stereo service in the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and ...
on Saturday 31 August 1991 (see
1991 in television 1991 in television may refer to: *1991 in American television * 1991 in Australian television * 1991 in Belgian television * 1991 in Brazilian television * 1991 in British television * 1991 in Canadian television * 1991 in Danish television * 199 ...
) though other UK broadcasters ITV and
Channel 4 Channel 4 is a British free-to-air public broadcast television network operated by the state-owned Channel Four Television Corporation. It began its transmission on 2 November 1982 and was established to provide a fourth television service ...
advertised this capability some months earlier. Channel 4 began tests much earlier in February 1989 via the Crystal Palace transmitter in London. It has been standardized as ETS EN 300 163.


Nations and regions using NICAM public broadcasts

Several European countries had implemented NICAM with the PAL and
SECAM SECAM, also written SÉCAM (, ''Séquentiel de couleur à mémoire'', French for ''color sequential with memory''), is an analog color television system that was used in France, some parts of Europe and Africa, and Russia. It was one of th ...
TV systems *
Belgium Belgium, ; french: Belgique ; german: Belgien officially the Kingdom of Belgium, is a country in Northwestern Europe. The country is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeast, France to ...
(analogue cable systems only; terrestrial switched to
DVB-T DVB-T, short for Digital Video Broadcasting – Terrestrial, is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 and first broadcast in Singapore in Feb ...
) *
Denmark ) , song = ( en, "King Christian stood by the lofty mast") , song_type = National and royal anthem , image_map = EU-Denmark.svg , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of Denmark , establish ...
(historical, switched to DVB-T and DVB-C) *
Estonia Estonia, formally the Republic of Estonia, is a country by the Baltic Sea in Northern Europe. It is bordered to the north by the Gulf of Finland across from Finland, to the west by the sea across from Sweden, to the south by Latvia, an ...
(historical, switched to DVB-T and DVB-C) *
Finland Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of Bot ...
(historical, switched to DVB-T and DVB-C) *
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
(historical, switched to DVB-T) *
Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders wi ...
(
ANT1 Antenna, better known as ANT1, is a television network airing in Greece. The alternate spelling is wordplay in Greek; ''ena'' (ένα) is the Greek number ''1'' (one), thus ''ANT1'' is pronounced the same as ''Antenna'' (Αντέννα). It laun ...
,
New Hellenic Television ERT2 ( el, ΕΡΤ2, "ERT Dyo") is a Greek free-to-air television channel owned and operated by state-owned public broadcaster Hellenic Broadcasting Corporation ( el, EPT – Ελληνική Ραδιοφωνία Τηλεόραση). It is the co ...
, ET3 and ET1 - historical, switched to DVB-T) *
Hungary Hungary ( hu, Magyarország ) is a landlocked country in Central Europe. Spanning of the Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the south, Cr ...
(historical, switched to DVB-T) *
Iceland Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its ...
(historical, switched to DVB-T) *
Ireland Ireland ( ; ga, Éire ; Ulster-Scots: ) is an island in the North Atlantic Ocean, in north-western Europe. It is separated from Great Britain to its east by the North Channel, the Irish Sea, and St George's Channel. Ireland is the s ...
(historical, switched to DVB-T. Analogue cable channels may still carry NICAM audio. However, these are digitally sourced channels re-encoded as PAL with NICAM at the headend.) *
Luxembourg Luxembourg ( ; lb, Lëtzebuerg ; french: link=no, Luxembourg; german: link=no, Luxemburg), officially the Grand Duchy of Luxembourg, ; french: link=no, Grand-Duché de Luxembourg ; german: link=no, Großherzogtum Luxemburg is a small lan ...
(switched to DVB-T; cable?) *
Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of ...
(historical, switched to DVB-T and DVB-C) *
Poland Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populou ...
(Analogue cable systems only; terrestrial switched to DVB-T) *
Portugal Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country whose mainland is located on the Iberian Peninsula of Southwestern Europe, and whose territory also includes the Atlantic archipelagos of th ...
(historical, switched to DVB-T) *
Romania Romania ( ; ro, România ) is a country located at the crossroads of Central Europe, Central, Eastern Europe, Eastern, and Southeast Europe, Southeastern Europe. It borders Bulgaria to the south, Ukraine to the north, Hungary to the west, S ...
(historical, switched to DVB-T2, cable?) *
Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-ei ...
(historical, switched to DVB-T2; still used in some local cable TV networks) *
Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = '' Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , ...
(historical, switched to DVB-T) *
Sri Lanka Sri Lanka (, ; si, ශ්‍රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...
*
Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic countries, Nordic c ...
(historical, switched to DVB-T and DVB-C) *
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and ...
(historical, switched to DVB-T) Some Asia-Pacific nations and regions have implemented NICAM *
Hong Kong Hong Kong ( (US) or (UK); , ), officially the Hong Kong Special Administrative Region of the People's Republic of China (abbr. Hong Kong SAR or HKSAR), is a List of cities in China, city and Special administrative regions of China, special ...
(commonly used for dual language for programming containing both Cantonese and English/Mandarin/Japanese/Korean soundtracks; full switchover to DTMB with Dolby AC-3 audio encoding complete by 1 December 2020, NICAM became historical from that date) *
Singapore Singapore (), officially the Republic of Singapore, is a sovereign island country and city-state in maritime Southeast Asia. It lies about one degree of latitude () north of the equator, off the southern tip of the Malay Peninsula, bor ...
(Full switchover to DVB-T2 and DVB-C complete by 1 January 2019. NICAM became historical from that date.) *
Macau Macau or Macao (; ; ; ), officially the Macao Special Administrative Region of the People's Republic of China (MSAR), is a city and special administrative region of China in the western Pearl River Delta by the South China Sea. With a pop ...
*
Guangzhou Guangzhou (, ; ; or ; ), also known as Canton () and Chinese postal romanization, alternatively romanized as Kwongchow or Kwangchow, is the Capital city, capital and largest city of Guangdong Provinces of China, province in South China, sou ...
*
Beijing } Beijing ( ; ; ), Chinese postal romanization, alternatively romanized as Peking ( ), is the Capital city, capital of the China, People's Republic of China. It is the center of power and development of the country. Beijing is the world's Li ...
( BTV) *
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...
( SABC 1, SABC 2, e.tv) *
Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federal constitutional monarchy consists of thirteen states and three federal territories, separated by the South China Sea into two regions: Peninsular Malaysia and Borneo's East Mal ...
** Formerly used by TV1, TV2, ntv7, 8TV, and TV9 around Klang Valley.
TV3 Channel 3 or TV 3 may refer to: Television * Canal 3 (Burkina Faso), a commercial television channel in Burkina Faso * Canal 3 (Guatemala), a commercial television channel in Guatemala * Channel 3 (Algeria), a public Algerian TV channel owned by E ...
also used NICAM on their VHF transmission frequency (Channel 12) in the Klang Valley, but used Zweikanalton on their UHF transmission frequency (Channel 29). Analog shutdown complete by 1 January 2019, thus NICAM and Zweikanalton broadcast became historical from that date. *
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island coun ...
(Full switchover to DVB-T complete by 1 December 2013. NICAM became historical from that date.) *
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Gui ...
** Television stations in Indonesia use NICAM Stereo for analogue television. Full switchover to DVB-T2 is expected to complete by 2020s by which all analogue broadcasting have ceased. *
Thailand Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is b ...
** Used on Channel 3 and
Channel 9 MCOT HD MCOT HD (in Thailand called Channel 9 MCOT HD th, ช่อง 9 เอ็มคอตเอชดี) is a Thai free-to-air television network launched on 24 June 1955 and owned by MCOT. History The channel was originally launched as Cha ...
(Except Thai PBS usually broadcast in stereo but analogue broadcast has been cease on 16 June 2018; Switched to terrestrial
DVB-T2 DVB-T2 is an abbreviation for "Digital Video Broadcasting – Second Generation Terrestrial"; it is the extension of the television standard DVB-T, issued by the consortium DVB, devised for the broadcast transmission of digital terrestrial tele ...
) Some other countries use Zweikanalton analogue stereo instead. Analogue stereo conversion thus begins.


Implementations

No consumer grade equipment capable of NICAM modulation is presently known. Below is a non-exhaustive list of broadcast grade equipment capable of NICAM coding and or modulation: * Philips PM5685/PM5686/PM5686A * Philips PM5687 * Eiden 198A * Pye/Varian/BBC
Sound-in-Syncs Sound-in-Syncs is a method of multiplexing sound and video signals into a channel designed to carry video, in which data representing the sound is inserted into the line synchronising pulse of an analogue television waveform. This is used on point ...
solution * IBA/RE Communications
Sound-in-Syncs Sound-in-Syncs is a method of multiplexing sound and video signals into a channel designed to carry video, in which data representing the sound is inserted into the line synchronising pulse of an analogue television waveform. This is used on point ...
solution * Tektronix 728E * Rohde & Schwarz SBUF-E NICAM Module * Barco NE-728


Operation

In order to provide
mono Mono may refer to: Common meanings * Infectious mononucleosis, "the kissing disease" * Monaural, monophonic sound reproduction, often shortened to mono * Mono-, a numerical prefix representing anything single Music Performers * Mono (Japanes ...
"compatibility", the NICAM signal is transmitted on a
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 broa ...
alongside the sound carrier. This means that the FM or AM regular mono sound carrier is left alone for reception by monaural receivers. A NICAM-based stereo-TV infrastructure can transmit a stereo TV programme as well as the mono "compatibility" sound at the same time, or can transmit two or three entirely different sound streams. This latter mode could be used to transmit audio in different languages, in a similar manner to that used for
in-flight movie In-flight entertainment (IFE) refers to the entertainment available to aircraft passengers during a flight. In 1936, the airship '' Hindenburg'' offered passengers a piano, lounge, dining room, smoking room, and bar during the -day flight betwee ...
s on international flights. In this mode, the user can select which soundtrack to listen to when watching the content by operating a "sound-select" control on the receiver. This is the spectrum of NICAM on the PAL system. On the SECAM L system, the NICAM sound carrier is at 5.85 MHz, before the AM sound carrier, and the video bandwidth is reduced from 6.5 MHz to 5.5 MHz. NICAM currently offers the following possibilities. The mode is automatically selected by the inclusion of a 3-bit type field in the data stream. * One digital stereo sound channel. * Two completely different digital mono sound channels. * One digital mono sound channel and a 352 kbit/s data channel. * One 704 kbit/s data channel. The four other options could be implemented at a later date. Only the first two of the ones listed are known to be in general use however.


NICAM packet transmission

The NICAM packet (except for the header) is scrambled with a nine-bit pseudo-random bit-generator before transmission. * The topology of this pseudo-random generator yields a bitstream with a repetition period of 511 bits. * The pseudo-random generator's
polynomial In mathematics, a polynomial is an expression consisting of indeterminates (also called variables) and coefficients, that involves only the operations of addition, subtraction, multiplication, and positive-integer powers of variables. An exampl ...
is: x^9 + x^4 + 1. * The pseudo-random generator is initialized with: 111111111. Making the NICAM bitstream look more like
white noise In signal processing, white noise is a random signal having equal intensity at different frequencies, giving it a constant power spectral density. The term is used, with this or similar meanings, in many scientific and technical disciplines ...
is important because this reduces signal patterning on adjacent TV channels. * The NICAM header is not subject to scrambling. This is necessary so as to aid in locking on to the NICAM data stream and resynchronisation of the data stream at the receiver. * At the start of each NICAM packet the pseudo-random bit generator's shift register is reset to all ones.


NICAM transmission problems

There are some latent issues involved with the processing of NICAM audio in the transmission chain. * NICAM (unlike the Compact Disc standard) samples 14-bit audio at 32 kHz. * The upper frequency limit of a NICAM sound channel is 15 kHz due to anti-aliasing filters at the encoder. * The original 14-bit PCM audio samples are companded digitally to 10 bits for transmission. * NICAM audio samples are divided into blocks of 32. If all the samples in a block are quiet, such that the most significant bits are all zeros, these bits can be discarded at no loss. * On louder samples some of the
least significant bit In computing, bit numbering is the convention used to identify the bit positions in a binary number. Bit significance and indexing In computing, the least significant bit (LSB) is the bit position in a binary integer representing the binar ...
s are truncated, with the hope that they will be inaudible. * A 3-bit control signal for each block records which bits were discarded. * Digital companding (using a CCITT J.17 pre-emphasis curve) ensures that the encoding and decoding algorithms can track perfectly.


NICAM carrier power

ITU (and CCITT) standards specify that the power level of the NICAM signal should be at -20 dB with respect to the power of the vision carrier. * The level of the FM mono sound carrier must be at least -13 dB. * Measuring the modulation level of the NICAM signal is difficult because the QPSK NICAM carrier waveform (unlike AM or FM modulated carrier waveforms) is not emitted at a discrete frequency. When measured with spectrum analyser the actual level of the carrier (L) can be calculated using the following formula: L(NICAM) = L(Measured) + 10 log (R/BWAnalyser) + K # L(NICAM) = actual level of the NICAM carrier BμV# L(Measured) = measured level of the NICAM carrier BμV# R = -3 dB bandwidth of the signal Hz# BWAnalyser = bandwidth of the spectrum analyser Hz# K = logarithmic form factor of the spectrum analyser ~2 dB note: if BWAnalyser is greater than R, the formula becomes L(NICAM) = L(Measured) + K


Differing features

NICAM sampling is not standard
PCM Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the am ...
sampling, as commonly employed with the
Compact Disc The compact disc (CD) is a digital optical disc data storage format that was co-developed by Philips and Sony to store and play digital audio recordings. In August 1982, the first compact disc was manufactured. It was then released in O ...
or at the codec level in MP3, AAC or Ogg audio devices. NICAM sampling more closely resembles Adaptive Differential Pulse Code Modulation, or
A-law An A-law algorithm is a standard companding algorithm, used in European 8-bit PCM digital communications systems to optimize, i.e. modify, the dynamic range of an analog signal for digitizing. It is one of two versions of the G.711 standar ...
companding with an extended, rapidly modifiable dynamic range.


Two's complement signing

The
two's complement Two's complement is a mathematical operation to reversibly convert a positive binary number into a negative binary number with equivalent (but negative) value, using the binary digit with the greatest place value (the leftmost bit in big- endian ...
method of signing the samples is used, so that: * 01111111111111 represents positive full-scale * 10000000000000 represents negative full-scale


±0 V has three binary representations

* 00000000000001 represents 0 V, with no +/- distinction. This may have originated as a method to reduce the emergence of DC patterns from transmission of silent material. * 00000000000000 represents 0 V, with no +/- distinction * 11111111111111 represents 0 V, with no +/- distinction


Parity checking limited to only 6 of 10 bits

In order to strengthen parity protection for the sound samples, the parity bit is calculated on only the top six bits of each NICAM sample. Early BBC NICAM research showed that uncorrected errors in the least significant four bits were preferable to the reduced overall protection offered by parity-protecting all ten bits.


Recording


VCR

VHS and
Betamax Betamax (also known as Beta, as in its logo) is a consumer-level analog recording and cassette format of magnetic tape for video, commonly known as a video cassette recorder. It was developed by Sony and was released in Japan on May 10, 1975, ...
home
videocassette recorder A videocassette recorder (VCR) or video recorder is an electromechanical device that records analog audio and analog video from broadcast television or other source on a removable, magnetic tape videocassette, and can play back the reco ...
s (VCRs) initially only recorded the audio tracks by means of a fixed linear recording head, which was inadequate for recording NICAM audio; this significantly limited their sound quality. Many VCRs later included high quality stereo audio recording as an additional feature, in which the incoming high quality stereo audio source (typically
FM radio FM broadcasting is a method of radio broadcasting using frequency modulation (FM). 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 cap ...
or NICAM TV) was frequency modulated and then recorded, in addition to the usual audio and video VCR tracks, using the same high-bandwidth
helical scan Helical scan is a method of recording high-frequency signals on magnetic tape. It is used in open-reel video tape recorders, video cassette recorders, digital audio tape recorders, and some computer tape drive A tape drive is a data sto ...
ning technique used for the video signal. Full-size VCRs already made full use of the tape, so the high quality audio signal was recorded diagonally ''under'' the video signal, using additional
helical scan Helical scan is a method of recording high-frequency signals on magnetic tape. It is used in open-reel video tape recorders, video cassette recorders, digital audio tape recorders, and some computer tape drive A tape drive is a data sto ...
heads and depth multiplexing. The mono audio track (and on some machines, a non-NICAM, non-Hi-Fi stereo track) was also recorded on the linear track, as before, to ensure backwards-compatibility of recordings made on Hi-Fi machines when played on non-Hi-Fi VCRs. Such devices were often described as "HiFi audio", "Audio FM" / "AFM" (FM standing for "Frequency Modulation") and sometimes informally as "Nicam" VCRs (due to their use in recording the Nicam broadcast audio signal). They remained compatible with non-HiFi VCR players since the standard audio track was also recorded, and were at times used as an alternative to
audio cassette tape The Compact Cassette or Musicassette (MC), also commonly called the tape cassette, cassette tape, audio cassette, or simply tape or cassette, is an analog magnetic tape recording format for audio recording and playback. Invented by Lou Otten ...
s due to their superior frequency range and flat frequency response.


DVD

While recording in video mode (compatible with
DVD-Video DVD-Video is a consumer video format used to store digital video on DVD discs. DVD-Video was the dominant consumer home video format in Asia, North America, Europe, and Australia in the 2000s until it was supplanted by the high-definition Blu- ...
), most DVD recorders can only record one of the three channels (Digital I, Digital II, Analogue mono) allowed by the standard. Newer standard such as
DVD-VR The DVD-VR standard defines a logical format for video recording on DVD-R, DVD-RW, and DVD-RAM style media, including the dual layer versions of these media. As opposed to media recorded with the DVD+VR recording standard, the resulting media are n ...
allows recording all the digital channels (in both stereo and bilingual mode), whereas the mono channel will be lost.


Flash memory and computer multimedia

Codecs for digital media on computers will often convert NICAM to another digital audio format to save drive space.


See also

* Multichannel television sound *
Sound-in-Syncs Sound-in-Syncs is a method of multiplexing sound and video signals into a channel designed to carry video, in which data representing the sound is inserted into the line synchronising pulse of an analogue television waveform. This is used on point ...
*
VIMCAS VIMCAS, standing for Vertical Interval Multiple Channel Audio System, is a dual-channel Sound-in-Syncs mechanism for transmitting digitally encoded audio in a composite video analogue television signal. Invented by Australian company IRT in the 198 ...
* Zweikanalton A2


References


Further reading

* Osborne, D.W. and Croll, M.G. (1973)
''Digital sound signals: Bit-rate reduction using an experimental digital compandor''.
BBC Research Department Report 1973/41. * Croll, M.G., Osborne, D.W. and Reid, D.F. (1973)
''Digital sound signals: Multiplexing six high-quality sound channels for transmission at a bit-rate of 2.048 Mbit/s''.
BBC Research Department Report 1973/42. * Reid, D.F. and Croll, M.G. (1974)
''Digital sound signals: The effect of transmission errors in a near-instantaneous digitally companded system''.
BBC Research Department Report 1974/24. * Reid, D.F. and Gilchrist, N.H.C. (1977)
''Experimental 704 kbit/s multiplex equipment for two 15 kHz sound channels''.
BBC Research Department Report 1977/38. * Kalloway, M.J. (1978)
''An experimental 4-phase d.p.s.k. stereo sound system: the effect of multipath propagation''.
BBC Research Department Report 1978/15.


External links

Related websites or technical explanations


The BBC's information page on NICAM



MATLAB NICAM function
{{Analogue TV transmitter topics Audio codecs BBC Research & Development Broadcast engineering Sound Television technology Television transmission standards British inventions 1978 introductions 1986 introductions 1991 introductions Audiovisual introductions in 1991