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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 size ...
for
digital audio Digital audio is a representation of sound recorded in, or converted into, digital signal (signal processing), digital form. In digital audio, the sound wave of the audio signal is typically encoded as numerical sampling (signal processing), ...
. 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, commonly shortened to 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 configurat ...
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 telecommunications 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 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: Science and technology * Multiplex communication, combining many signals into one transmission circuit or channel ** Multiplex (television), a group of digital television or radio channels that are combined for broadcast * ...
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 companding to compress 14-bit linear PCM samples into 10 bits (14:10) * A NICAM-type system proposed by Télédiffusion de France (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 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 amplitud ...
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 The British Broadcasting Corporation (BBC) is a British public service broadcaster headquartered at Broadcasting House in London, England. Originally established in 1922 as the British Broadcasting Company, it evolved into its current sta ...
. 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, commonly shortened to 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 configurat ...
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 Saturday 31 August 1991, by which time 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. coming as many as 18 months after ITV and
Channel 4 Channel 4 is a British free-to-air public broadcast television channel owned and operated by Channel Four Television Corporation. It is state-owned enterprise, publicly owned but, unlike the BBC, it receives no public funding and is funded en ...
had begun advertising this capability to coincide with the Independent Broadcasting Authority rolling out NICAM on a transmitter-by-transmitter basis which had begun in 1989 with the Crystal Palace and Emley Moor transmitters. 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 ''sequential colour memory''), is an analog color television system that was used in France, Russia and some other countries or territories of Europe and Africa. ...
TV systems *
Belgium Belgium, officially the Kingdom of Belgium, is a country in Northwestern Europe. Situated in a coastal lowland region known as the Low Countries, it is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeas ...
(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 Fe ...
) *
Croatia Croatia, officially the Republic of Croatia, is a country in Central Europe, Central and Southeast Europe, on the coast of the Adriatic Sea. It borders Slovenia to the northwest, Hungary to the northeast, Serbia to the east, Bosnia and Herze ...
(historical, switched to DVB-T and later DVB-T2, analog cable seems to either be mono or use analog A2 stereo) *
Denmark Denmark is a Nordic countries, Nordic country in Northern Europe. It is the metropole and most populous constituent of the Kingdom of Denmark,, . also known as the Danish Realm, a constitutionally unitary state that includes the Autonomous a ...
(historical, switched to DVB-T and DVB-C) *
Estonia Estonia, officially the Republic of Estonia, is a country in Northern Europe. It is bordered to the north by the Gulf of Finland across from Finland, to the west by the Baltic Sea across from Sweden, to the south by Latvia, and to the east by Ru ...
(historical, switched to DVB-T and DVB-C) *
Finland Finland, officially the Republic of Finland, is a Nordic country in Northern Europe. It borders Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of Bothnia to the west and the Gulf of Finland to the south, ...
(historical, switched to DVB-T and DVB-C) *
France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
(historical, switched to DVB-T) *
Greece Greece, officially the Hellenic Republic, is a country in Southeast Europe. Located on the southern tip of the Balkan peninsula, it shares land borders with Albania to the northwest, North Macedonia and Bulgaria to the north, and Turkey to th ...
( ANT1, New Hellenic Television, ET3 and ET1 - historical, switched to DVB-T) *
Hungary Hungary is a landlocked country in Central Europe. Spanning much of the Pannonian Basin, Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the south, Croatia and ...
(historical, switched to DVB-T) *
Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...
(historical, switched to DVB-T) *
Ireland Ireland (, ; ; Ulster Scots dialect, Ulster-Scots: ) is an island in the North Atlantic Ocean, in Northwestern Europe. Geopolitically, the island is divided between the Republic of Ireland (officially Names of the Irish state, named Irelan ...
(historical, switched to DVB-T, DVB-C and IPTV) *
Luxembourg Luxembourg, officially the Grand Duchy of Luxembourg, is a landlocked country in Western Europe. It is bordered by Belgium to the west and north, Germany to the east, and France on the south. Its capital and most populous city, Luxembour ...
(switched to DVB-T; cable?) *
Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. The remote Arctic island of Jan Mayen and the archipelago of Svalbard also form part of the Kingdom of ...
(historical, switched to DVB-T and DVB-C) *
Poland Poland, officially the Republic of Poland, is a country in Central Europe. It extends from the Baltic Sea in the north to the Sudetes and Carpathian Mountains in the south, bordered by Lithuania and Russia to the northeast, Belarus and Ukrai ...
(Analogue cable systems only; terrestrial switched to DVB-T) *
Portugal Portugal, officially the Portuguese Republic, is a country on the Iberian Peninsula in Southwestern Europe. Featuring Cabo da Roca, the westernmost point in continental Europe, Portugal borders Spain to its north and east, with which it share ...
(historical, switched to DVB-T) *
Romania Romania is a country located at the crossroads of Central Europe, Central, Eastern Europe, Eastern and Southeast Europe. It borders Ukraine to the north and east, Hungary to the west, Serbia to the southwest, Bulgaria to the south, Moldova to ...
(historical on terrestrial as switched to DVB-T2; on cable networks, still used by some operators providing analogue cable television) *
Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
*
Spain Spain, or the Kingdom of Spain, is a country in Southern Europe, Southern and Western Europe with territories in North Africa. Featuring the Punta de Tarifa, southernmost point of continental Europe, it is the largest country in Southern Eur ...
(historical, switched to DVB-T) *
South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...
( SABC 1, SABC 2, e.tv) *
Sweden Sweden, formally the Kingdom of Sweden, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. It borders Norway to the west and north, and Finland to the east. At , Sweden is the largest Nordic count ...
(historical, switched to DVB-T and DVB-C) *
Ukraine Ukraine is a country in Eastern Europe. It is the List of European countries by area, second-largest country in Europe after Russia, which Russia–Ukraine border, borders it to the east and northeast. Ukraine also borders Belarus to the nor ...
*
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...
(historical, switched to DVB-T) Some Asia-Pacific nations and regions have implemented NICAM *
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
**
Hong Kong Hong Kong)., Legally Hong Kong, China in international treaties and organizations. is a special administrative region of China. With 7.5 million residents in a territory, Hong Kong is the fourth most densely populated region in the wor ...
(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) **
Macau Macau or Macao is a special administrative regions of China, special administrative region of the People's Republic of China (PRC). With a population of about people and a land area of , it is the most List of countries and dependencies by p ...
(commonly used for dual language for programming containing both Cantonese and Portuguese/English/Mandarin/Japanese/Korean soundtracks; full switchover to DTMB with MPEG-1 Audio Layer II audio encoding complete by 30 June 2023, NICAM became historical from that date) *
Malaysia Malaysia is a country in Southeast Asia. Featuring the Tanjung Piai, southernmost point of continental Eurasia, it is a federation, federal constitutional monarchy consisting of States and federal territories of Malaysia, 13 states and thre ...
** Formerly used by TV1, TV2,
ntv7 Natseven TV Sdn Bhd, operating as NTV7 is a Malaysian free-to-air television channel owned by Media Prima, Media Prima Berhad. The third private commercial TV station in Malaysia, the network focused on the urban area with various types of ...
, 8TV, and TV9 around Klang Valley. TV3 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 () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
(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 Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...
** Most national television networks in Indonesia used NICAM for analogue television. Analog shutdown complete by August 12, 2023, thus NICAM became historical from that date. *
Singapore Singapore, officially the Republic of Singapore, is an island country and city-state in Southeast Asia. The country's territory comprises one main island, 63 satellite islands and islets, and one outlying islet. It is about one degree ...
(Used on Mediacorp Channel U. Full switchover to DVB-T2 complete by 1 January 2019. NICAM became historical from that date.) *
Sri Lanka Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka, also known historically as Ceylon, is an island country in South Asia. It lies in the Indian Ocean, southwest of the Bay of Bengal, separated from the Indian subcontinent, ...
*
Thailand Thailand, officially the Kingdom of Thailand and historically known as Siam (the official name until 1939), is a country in Southeast Asia on the Mainland Southeast Asia, Indochinese Peninsula. With a population of almost 66 million, it spa ...
** Used on Channel 3, Channel 9 MCOT HD and Thai PBS, usually broadcast in dual-sound mode with sometimes in stereo mode. All analogue television service ceased since March 26, 2020. Switchover to terrestrial DVB-T2 with HE-AAC v2 codec, NICAM became historical from that date. 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 solution * IBA/RE Communications Sound-in-Syncs solution * Tektronix 728E * Rohde & Schwarz SBUF-E NICAM Module * Barco NE-728 * CableWorld CW-3830


Operation

In order to provide mono "compatibility", the NICAM signal is transmitted on a subcarrier 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 movies 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. The spectrum of NICAM on the PAL system differs from that on the SECAM L system where 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 a Expression (mathematics), mathematical expression consisting of indeterminate (variable), indeterminates (also called variable (mathematics), variables) and coefficients, that involves only the operations of addit ...
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, i ...
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 bit In computing, bit numbering is the convention used to identify the bit positions in a binary numeral system, binary number. Bit significance and indexing In computing, the least significant bit (LSb) is the bit position in a Binary numeral sy ...
s are all zeros, these bits can be discarded at no loss. * On louder samples some of the least significant bits 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 sampling, as commonly employed with the
Compact Disc The compact disc (CD) is a Digital media, digital optical disc data storage format co-developed by Philips and Sony to store and play digital audio recordings. It employs the Compact Disc Digital Audio (CD-DA) standard and was capable of hol ...
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 companding with an extended, rapidly modifiable dynamic range.


Two's complement signing

The
two's complement Two's complement is the most common method of representing signed (positive, negative, and zero) integers on computers, and more generally, fixed point binary values. Two's complement uses the binary digit with the ''greatest'' value as the ''s ...
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, and stylized as the Greek letter Beta, β in its logo) is a discontinued consumer analog Videotape, video cassette recording format developed by Sony. It was one of the main competitors in the videotape format war ag ...
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 AV sources and can play back the recording after rewinding. The use of a VCR to 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 that uses frequency modulation (FM) of the radio broadcast carrier wave. Invented in 1933 by American engineer Edwin Armstrong, wide-band FM is used worldwide to transmit high fidelity, high-f ...
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 scanning 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 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 tapes due to their superior frequency range and flat
frequency response In signal processing and electronics, the frequency response of a system is the quantitative measure of the magnitude and Phase (waves), phase of the output as a function of input frequency. The frequency response is widely used in the design and ...
.


DVD

While recording in video mode (compatible with
DVD-Video DVD-Video is a consumer video format used to store digital video on DVDs. DVD-Video was the dominant consumer home video format in most of the world in the 2000s. As of 2024, it competes with the high-definition Blu-ray Disc, while both rece ...
), most
DVD recorder A DVD recorder is an optical disc recorder that uses optical disc recording technologies to digital recording, digitally record analog signal, analog or Digital signal (signal processing), digital signals onto blank writable DVD recordable, D ...
s can only record one of the three channels (Digital I, Digital II, Analogue mono) allowed by the standard. Newer standard such as DVD-VR 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 Multichannel Television Sound (MTS) is the method of encoding three additional audio channels into analog 4.5 MHz audio carriers on System M and System N.The system was developed by an industry group known as the Broadcast Television Systems ...
* Sound-in-Syncs * VIMCAS * 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