NICAM

Near Instantaneous Companded Audio Multiplex (NICAM) is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks.[1] In the 1980s, broadcasters began to use NICAM compression for transmissions of stereo 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).[2] The application of this to broadcasting, in which the companding was to be done entirely digitally after the ADC and before the DAC, was described in a 1972 BBC Research Report.[3]

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 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.[4][5]

Audio is encoded using 14 bit pulse-code modulation 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 it is sent over. It uses the same audio coding parameters as NICAM-3.

The first NICAM digital stereo programme was broadcast on BBC2 in 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 on Saturday 31 August 1991 (see 1991 in television) though other UK broadcasters ITV and Channel 4 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.[6]

Nations using NICAM public broadcasts

Several European countries (as well as one Asian country) have implemented NICAM with the PAL and SECAM TV systems[7][8][9]

  • Belgium (Analogue cable systems only; terrestrial switched to DVB-T)
  • Denmark (historical, switched to DVB-T and DVB-C)
  • Estonia (historical, switched to DVB-T)
  • Finland (historical, switched to DVB-T and DVB-C)
  • France (historical, switched to DVB-T)
  • Greece (ANT1, New Hellenic Television, ET3 and ET1 - historical, switched to DVB-T)
  • Hungary (historical, switched to DVB-T)
  • Iceland (historical, switched to DVB-T)
  • Ireland (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.)

Some Asia-Pacific nations have implemented NICAM

  • Hong Kong (commonly used for dual language for programming containing both Cantonese and English/Mandarin/Japanese/Korean soundtracks; planned to cease by 2020 when digital TV broadcasting transition is complete and analogue TV transmissions will be stopped)
  • Singapore (historical, switched to DVB-T2 and DVB-C)
  • Macau
  • Guangzhou
  • South Africa (SABC1, SABC2, etv)
  • Malaysia
    • Used by TV1, TV2, ntv7, 8TV, and TV9 around Klang Valley. TV3 also uses NICAM on their VHF transmission frequency (Channel 12) in the Klang Valley, but uses Zweikanalton on their UHF transmission frequency (Channel 29).
  • New Zealand (Full switchover to DVB-T complete by 1 December 2013. NICAM became historical from that date.)
  • Indonesia
    • Television stations in Indonesia use NICAM Stereo for analogue television. Full switchover to DVB-T2 is expected to complete by 2020 by which all analogue broadcasting have ceased.
  • Thailand

Some other countries use Zweikanalton analogue stereo instead. Analogue stereo conversion thus begins.

How NICAM works

In order to provide mono "compatibility", the NICAM signal is transmitted on a subcarrier alongside the sound carrier. This means that the FM 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.


This is the spectrum of NICAM on the PAL system. On the SECAM L system, the NICAM sound carrier is at 5.85 MHz, a point below the FM 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 is:
  • The pseudo-random generator is initialized with:

Making the NICAM bitstream look more like white noise 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 issues

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 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

  1. L(NICAM) = actual level of the NICAM carrier [dBμV]
  2. L(Measured) = measured level of the NICAM carrier [dBμV]
  3. R = -3 dB bandwidth of the signal [kHz]
  4. BWAnalyser = bandwidth of the spectrum analyser [kHz]
  5. 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

NICAM's unusual features

NICAM sampling is not standard PCM sampling, as commonly employed with the Compact Disc 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 method of signing the samples is used,[10] 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 of NICAM audio

VCR

VHS and Betamax home videocassette recorders ("VCR"s) initially only recorded the audio tracks using 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 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 exceptional bandwidth, frequency range, and extremely flat frequency response.

DVD

While recording in video mode (compatible with DVD-Video), 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 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 compress drive space.

See also

References

  1. ^ 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
  2. ^ Bartlett, C.J.C. and Greszczuk, J. (1964), Companding in a p.c.m. system. Symposium on Transmission Aspects of Communication Networks, London, IEE 1964, pp. 183–186.
  3. ^ Osborne, D.W. (1972) Digital sound signals: further investigation of instantaneous and other rapid companding systems. BBC Research Dept. Report 1972/31.
  4. ^ Jones, A.H. (1978), Digital coding of audio signals for point-to-point transmission. IEE Conference Publication No. 166, pp. 25–28
  5. ^ Gilchrist, N.H.C. (1978), Digital sound signals: tests to compare the performance of five companding systems for high-quality sound signals. BBC Research Department Report 1978/26.
  6. ^ ETSI ETS EN 300 163, (previously: EBU T 3266)
  7. ^ "Broadcasting System Details". University of Surrey – Department of Electronic Engineering. Archived from the original on December 5, 2010. Retrieved 2007-08-30.
  8. ^ Analogue TV technologies
  9. ^ World-Wide T.V. Standards
  10. ^ Steve Hosgood. ""All You Ever Wanted to Know About NICAM but were Afraid to Ask"". Archived from the original on February 14, 2005. Retrieved 2007-08-30.

Further reading

External links

Related websites or technical explanations

Analogue terrestrial television in the United Kingdom

Analogue terrestrial television in the United Kingdom was originally the method by which the significant majority of viewers in the UK, the Channel Islands and the Isle of Man received television. Analogue terrestrial television broadcasts have ceased everywhere in the UK with Northern Ireland being the last region to have ceased broadcasting analogue terrestrial television broadcasts. Northern Ireland switched off the last analogue television signals, making all of the United Kingdom only capable of receiving digital television, in the early hours of 24 October 2012. It has been completely replaced by digital terrestrial television and other non-terrestrial means as of the end of 2012.

Astra Digital Radio

Astra Digital Radio (ADR) was a system used by SES for digital radio transmissions on the early Astra satellites, using the audio subcarrier frequencies of analogue television channels. It was introduced in 1995. As of February 2008, there were still 51 stations transmitting in this format.

Broadcast television systems

Terrestrial television systems (or Broadcast television systems in the US and Canada) are the encoding or formatting standards for the transmission and reception of terrestrial television signals. There were three main analog television systems in use around the world until the late 2010s (expected): NTSC, PAL, and SECAM. Now in digital terrestrial television (DTT), there are four main systems in use around the world: ATSC, DVB, ISDB and DTMB.

CCIR System A

CCIR System A was the 405 line analog broadcast television system broadcast in the UK and Ireland. CCIR service was discontinued in 1985.

CCIR System B

CCIR System B was the 625-line analog broadcast television system which at its peak was the system used in most countries. It is being replaced across Western Europe, part of Asia and Africa by digital broadcasting.

CCIR System G

CCIR System G is an analog broadcast television system used in many countries. There are several systems in use and letter G is assigned for the European UHF system which is also used in the majority of Asian and African countries. (However some countries in Europe use different systems.)

CCIR System H

CCIR System H is an analog broadcast television system primarily used in Belgium, the Balkans and Malta on the UHF bands.

CCIR System I

CCIR System I is an analog broadcast television system. It was first used in the Republic of Ireland starting in 1962 as the 625-line broadcasting standard to be used on VHF Band I and Band III, sharing Band III with 405-line System A signals radiated in the north of the country. The UK started its own 625-line television service in 1964 also using System I, but on UHF only - the UK has never used VHF for 625-line television except for some cable relay distribution systems.

Since then, System I has been adopted for use by Hong Kong, Macau, the Falkland Islands and South Africa. The Republic of Ireland has (slowly) extended its use of System I onto the UHF bands.

As of late 2012, analog television is no longer transmitted in either the UK or the Republic of Ireland. South Africa expects to discontinue System I in 2013, and Hong Kong by 2020.

CCIR System M

CCIR (or FCC) System M, sometimes called 525 line, is the analog broadcast television system used in the United States since July 1, 1941, and also in most of the Americas and Caribbean, South Korea, and Taiwan. Japan uses System J, which is nearly identical to System M. The systems were given their letter designations in the ITU identification scheme adopted in Stockholm in 1961. Both System M and System J display 525 lines of video at 30 frames per second using 6 MHz spacing between channel numbers, and is used for both VHF and UHF channels.

Currently (as of 2015), System M and J is being replaced by digital broadcasting such as the Americas, Japan, South Korea, Taiwan and the Philippines.

EIAJ MTS

EIAJ MTS is a multichannel television sound standard created by the EIAJ.

Bilingual and stereo sound television programs started being broadcast in Japan in October 1978 using a system developed by NHK Technical Research Labs. This system was modified and standardized by the EIAJ in January 1979.

The original version M TV standard has a monaural FM transmission at 4.5 MHz. For Japanese multichannel television sound a second channel, or sub-channel, is added to the original signal by using an FM sub-carrier at twice the line frequency (Fh, or 15374 Hz). In order to identify the different modes (mono, stereo, or dual sound) a pilot tone is also added on an AM carrier at 3.5 times the line frequency. The pilot tone frequencies are 982.5 Hz for stereo and 922.5 Hz for dual sound. Contrary to Zweikanalton these pilot tones are not coupled to the line frequency but were instead chosen to allow use of filters already employed in the Pocket Bell pager system.

Multiplexed Analogue Components

Multiplexed analogue components (MAC) was a satellite television transmission standard, originally proposed for use on a Europe-wide terrestrial HDTV system, although it was never used terrestrially.

Netherlands Institute for the Classification of Audiovisual Media

Netherlands Institute for the Classification of Audiovisual Media (Nederlands Instituut voor de Classificatie van Audiovisuele Media) is the institute responsible for the content given for review for the Dutch motion picture rating system, Kijkwijzer, and the software given for review for the European video game content rating system PEGI.

Network packet

A network packet is a formatted unit of data carried by a packet-switched network. A packet consists of control information and user data, which is also known as the payload. Control information provides data for delivering the payload, for example: source and destination network addresses, error detection codes, and sequencing information. Typically, control information is found in packet headers and trailers.

In packet switching, the bandwidth of the communication medium is shared between multiple communication sessions, in contrast to circuit switching, in which circuits are preallocated for the duration of one session and data is typically transmitted as a continuous bit stream.

One-way voice link

A one-way voice link (OWVL) is typically a radio based communication method used by spy networks to communicate with agents in the field typically (but not exclusively) using shortwave radio frequencies.

Shortwave frequencies were and are generally highly preferred for their long range, as a communications link of 1200 km is easily possible. VHF and UHF frequencies can be used for one-way voice circuits, but are generally not preferred as their range is at best 300 km (on flat terrain). Since the 1970s infrared point-to-point communication systems have been used that offer OWVLs, but the number of users was always limited.

This communications system often employs recorders to transmit pre-recorded messages in real time or in burst transmissions, which minimize the time that a spy needs to be on the air. Voice-scrambling systems have been selectively used for this kind of communications circuit since the 1980s, based on operational needs.

Since personal computers became cheap and readily available in the 2000s, time compressed voice scrambling for one-way and bi-directional circuits is a practically free technology.

OWVLs have existed outside espionage, for example the NICAM transmission system was modified in the UK to allow for an OWVL to BBC mobile units. This OWVL was typically used for sports events, as it was highly flexible.

TVB Pearl

TVB Pearl (Chinese: 無綫電視明珠台) is one of the two free television services in Hong Kong that mainly broadcast in the English language, the other being ATV World and later ViuTVsix. It is owned and operated by Television Broadcasts Limited, and together with its sister Cantonese language station TVB Jade, is broadcast from TVB City at 77 Chun Choi Street in Tseung Kwan O Industrial Estate in Tseung Kwan O, in the Sai Kung District, which is in the Eastern region of Hong Kong's New Territories.

Apart from the use of English rather than Cantonese, TVB Pearl's daytime output differs from TVB Jade's in providing more serious programming, such as documentaries and news, and during peak viewing time it is much more reliant on overseas-made TV series and films. Occasionally, TVB Pearl also shows programmes in other languages (but usually well outside peak viewing time), including Mandarin, Japanese and Korean (see #Non-English programmes).

Established on 19 November 1967, TVB Pearl broadcasts free of charge to over 2.1 million households in Hong Kong.

The channel is operated by Television Broadcasts Limited or TVB, along with its sister channel TVB Jade.

In 1991, TVB Pearl began to broadcast in NICAM, a digital audio modulation system that provides a facility for stereo or bilingual or trilingual audio transmission. (For the digital counterpart, multiple AC-3 streams are transmitted for the same purpose.) With a compatible television, the viewer can receive audio in their choice of language; typically, English and Cantonese. Chinese subtitles are available on most programmes after 18:20.

The transmission of TVB Pearl digital TV channel have been upgraded from SDTV to HDTV video format on 28 October 2012 at 02:50.

TVNZ

Television New Zealand (Māori: Te Reo Tātaki o Aotearoa), more commonly referred to as TVNZ, is a state-owned television network that is broadcast throughout New Zealand and parts of the Pacific region. Although the network identifies as a national, part-public broadcaster, it is fully commercially funded.

TVNZ was competition free until November 1989 when private channel TV3 (now Three) was launched. This began the battle for ratings with the only real rival MediaWorks New Zealand, which currently operates channels Three, ThreeLife, Bravo, and The Edge TV. However, TVNZ still maintains a number of transmission advantages due to its long-standing relationship with the state-owned sister company Kordia.

TVNZ operates playout services from its Auckland studio via Kordia's fibre and microwave network for TVNZ 1, TVNZ 2 and TVNZ Duke, with new media video services via the American-owned Brightcove which is streamed on the Akamai RTMP/HLS DNS based caching network. Its former channels include TVNZ Kidzone (closed 30 April 2016), TVNZ Heartland (closed 31 May 2015), TVNZ U (closed August 2013), TVNZ 7 (closed June 2012), TVNZ 6 (closed 2011), and TVNZ Sport Extra (closed 2009).

Approximately 90% of TVNZ's revenue is from commercial activity (such as advertising and merchandising). The remainder of its funding comes from government funding agencies.

VIT signals

In television broadcasting, VIT signals (vertical interval test signals) are a group of test signals inserted in the composite video signal. These signals are used to weight the transmission characteristics of the system between the test generator and the output of the demodulator, where the system includes the microwave links, or TVROs as well as the TV transmitters and the transposers. There are both ATSC and EBU standards for VIT. (Because analogue television is being phased out globally, VIT standards are considered superseded.)

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 recording. Use of a VCR to record a television program to play back at a more convenient time is commonly referred to as timeshifting. VCRs can also play back prerecorded tapes. In the 1980s and 1990s, prerecorded videotapes were widely available for purchase and rental, and blank tapes were sold to make recordings.

Most domestic VCRs are equipped with a television broadcast receiver (tuner) for TV reception, and a programmable clock (timer) for unattended recording of a television channel from a start time to an end time specified by the user. These features began as simple mechanical counter-based single-event timers, but were later replaced by more flexible multiple-event digital clock timers. In later models the multiple timer events could be programmed through a menu interface displayed on the playback TV screen ("on-screen display" or OSD). This feature allowed several programs to be recorded at different times without further user intervention, and became a major selling point.

Zweikanalton

Zweikanalton ("two-channel sound") or A2 Stereo, is an analog television sound transmission system used in Germany, Austria, Australia, Switzerland, Netherlands and other countries that use or used PAL-B or PAL-G. South Korea formerly utilised its variant of this format in analogue television system until 31 December 2012. It relies on two separate FM carriers.

This offers a relatively high separation between the channels (compared to a subcarrier-based multiplexing system) and can thus be used for bilingual broadcasts as well as stereo. Unlike the competing NICAM standard, Zweikanalton is an analog system.

Systems
Color systems
Video
Sound
Modulation
Transmission
Frequencies & Bands
Propagation
Testing
Artifacts

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