View source for NICAM

{{short description|Digital audio compression standard}}
{{about|a compression form for digital audio|the media content rating institute|Netherlands Institute for the Classification of Audiovisual Media}}
{{Use dmy dates|date=April 2022}}

'''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.<ref name="croll">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</ref> In the 1980s, broadcasters began to use NICAM compression for transmissions of [[Stereophonic sound|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 [[Analog-to-digital converter|analogue-to-digital converter (ADC)]] and after the [[Digital-to-analog converter|digital-to-analogue converter (DAC)]].<ref>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.</ref> 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.<ref>Osborne, D.W. (1972) [http://www.bbc.co.uk/rd/publications/rdreport_1972_31 ''Digital sound signals: further investigation of instantaneous and other rapid companding systems''.] BBC Research Dept. Report 1972/31.</ref>

=== Point-to-point links ===
NICAM was originally intended to provide broadcasters with six high-quality audio channels within a total [[Bandwidth (computing)|bandwidth]] of 2048&nbsp;kbit/s. This figure was chosen to match the [[E-carrier level 1|E1]] primary [[Multiplexing|multiplex]] rate, and systems using this rate could make use of the planned [[Plesiochronous Digital Hierarchy|PDH]] national and international telecommunications networks.

Several similar systems had been developed in various countries, and in about 1977/78 the [[BBC Research|BBC Research Department]] conducted listening tests to evaluate them. The candidates were:
* A [[RAI]] system which used [[A-law]] companding to compress 14-bit [[Pulse-code modulation|linear PCM]] [[sampling (signal processing)|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.<ref name="jones">Jones, A.H. (1978), ''Digital coding of audio signals for point-to-point transmission''. IEE Conference Publication No. 166, pp. 25–28</ref><ref>Gilchrist, N.H.C. (1978), [http://www.bbc.co.uk/rd/publications/rdreport_1978_26 ''Digital sound signals: tests to compare the performance of five companding systems for high-quality sound signals''.] BBC Research Department Report 1978/26.</ref>

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&nbsp;kbit/s [[bitstream]] it is sent over. It uses the same audio coding parameters as NICAM-3.

The first NICAM digital [[stereophonic sound|stereo]] programme was the [[The Proms|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 (TV network)|ITV]] and [[Channel 4]] 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 transmitting station|Emley Moor]] transmitters.<ref>[https://www.youtube.com/watch?v=f9-bnNFPArI&ab_channel=bayside2000  IBA Engineering Announcement 19 December 1989]</ref>

It has been standardized as ETS EN 300 163.<ref>[http://www.etsi.org/ ETSI] ETS EN 300 163, (previously: [http://www.ebu.ch EBU] T 3266)</ref>

==== Nations and regions using NICAM public broadcasts ====
Several European countries had implemented NICAM with the [[PAL]] and [[SECAM]] TV systems<ref>{{cite web|url=http://www.ee.surrey.ac.uk/Contrib/WorldTV/broadcast.html |title=Broadcasting System Details |publisher=University of Surrey – Department of Electronic Engineering |access-date=2007-08-30 |url-status=dead |archive-url=https://web.archive.org/web/20101205071827/http://www.ee.surrey.ac.uk/Contrib/WorldTV/broadcast.html |archive-date=December 5, 2010 }}</ref><ref>[http://home.tiscalinet.ch/hahn/atvt.html Analogue TV technologies]</ref><ref>[http://www.videouniversity.com/standard.htm World-Wide T.V. Standards]</ref>
* [[Belgium]] (analogue cable systems only; terrestrial switched to [[DVB-T]])
* [[Croatia]] (historical, switched to DVB-T and later DVB-T2, analog cable seems to either be mono or use analog A2 stereo)
* [[Denmark]] (historical, switched to DVB-T and DVB-C)
* [[Estonia]] (historical, switched to DVB-T and DVB-C)
* [[Finland]] (historical, switched to DVB-T and DVB-C)
* [[France]] (historical, switched to DVB-T)
* [[Greece]] ([[ANT1]], [[New Hellenic Television]], [[ET3 (Greece)|ET3]] and [[ET1 (Greece)|ET1]] - historical, switched to DVB-T)
* [[Hungary]] (historical, switched to DVB-T)
* [[Iceland]] (historical, switched to DVB-T)
* [[Republic of Ireland|Ireland]] (historical, switched to DVB-T, DVB-C and IPTV)
* [[Luxembourg]] (switched to DVB-T; cable?)
* [[Norway]] (historical, switched to DVB-T and DVB-C)
* [[Poland]] (Analogue cable systems only; terrestrial switched to DVB-T)
* [[Portugal]] (historical, switched to DVB-T)
* [[Romania]] (historical on terrestrial as switched to DVB-T2; on cable networks, still used by some operators providing analogue cable television)
* [[Russia]]
* [[Spain]] (historical, switched to DVB-T)
* [[South Africa]] ([[SABC 1]], [[SABC 2]], [[e.tv]])
* [[Sweden]] (historical, switched to DVB-T and DVB-C)
* [[Ukraine]]
* [[United Kingdom]] (historical, switched to DVB-T)

Some Asia-Pacific nations and regions have implemented NICAM
* [[China]]
** [[Hong Kong]] (commonly used for dual language for programming containing both Cantonese and English/Mandarin/Japanese/Korean soundtracks; full switchover to [[Digital Terrestrial Multimedia Broadcast|DTMB]] with Dolby AC-3 audio encoding complete by 1 December 2020, NICAM became historical from that date)
** [[Macau]] (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]]
** Formerly used by [[Radio Televisyen Malaysia|TV1, TV2]], [[ntv7]], [[8TV (Malaysia)|8TV]], and [[TV9 (Malaysia)|TV9]] around Klang Valley. [[TV3 (Malaysia)|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]] (Full switchover to DVB-T complete by 1 December 2013. NICAM became historical from that date.)
* [[Indonesia]]
** 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]] (Used on [[Mediacorp Channel U]]. Full switchover to DVB-T2 complete by 1 January 2019. NICAM became historical from that date.)
* [[Sri Lanka]]
* [[Thailand]]
** Used on [[Channel 3 (Thailand)|Channel 3]], [[Channel 9 MCOT HD]] and [[Thai Public Broadcasting Service|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.<ref>{{cite web | url=https://www.vintage-radio.net/forum/showthread.php?t=191028 | title=Consumer NICAM Modulators. Did any exist? }}</ref> Below is a non-exhaustive list of broadcast grade equipment capable of NICAM coding and or modulation:

* Philips PM5685/PM5686/PM5686A<ref>{{cite web | url=https://www.mattmillman.com/info/list-of-known-nicam-728-encoders/ | title=List of known NICAM-728 Encoders }}</ref>
* Philips PM5687<ref>{{cite web | url=https://www.mattmillman.com/remembering-nicam-part-1-broadcast-equipment-teardown/ | title=Remembering NICAM Part 1: Broadcast Equipment Teardown | date=4 June 2022 }}</ref>
* Eiden 198A<ref>{{cite web | url=https://www.mattmillman.com/info/list-of-known-nicam-728-encoders/ | title=List of known NICAM-728 Encoders }}</ref>
* [[Pye (electronics company)|Pye]]/Varian/BBC [[Sound-in-Syncs]] solution<ref>{{cite web | url=https://www.mattmillman.com/examining-the-sort-of-bbcs-sound-in-sync-nicam-728-broadcast-solution/ | title=Examining the (sort-of) BBC's Sound-in-Sync (NICAM-728) Broadcast solution }}</ref>
* [[Independent Broadcasting Authority|IBA]]/RE Communications  [[Sound-in-Syncs]] solution<ref>{{cite web | url=https://www.youtube.com/watch?v=l1xVgxmns90 | title=IBA Engineering Announcements - Graham Sawdy on NICAM - 20 March 1990 | website=[[YouTube]] | date=5 March 2014 }}</ref>
* Tektronix 728E<ref>{{cite web | url=https://www.mattmillman.com/info/list-of-known-nicam-728-encoders/ | title=List of known NICAM-728 Encoders }}</ref>
* Rohde & Schwarz SBUF-E NICAM Module<ref>{{cite web | url=https://www.mattmillman.com/info/list-of-known-nicam-728-encoders/ | title=List of known NICAM-728 Encoders }}</ref>
* Barco NE-728<ref>{{cite web | url=https://www.mattmillman.com/info/list-of-known-nicam-728-encoders/ | title=List of known NICAM-728 Encoders }}</ref>
* CableWorld CW-3830

==Operation==
In order to provide [[Monaural|mono]] "compatibility", the NICAM signal is transmitted on a [[subcarrier]] alongside the sound carrier. This means that the [[Frequency modulation|FM]] or [[Amplitude modulation|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]]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.

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&nbsp;MHz, before the AM sound carrier, and the video bandwidth is reduced from 6.5&nbsp;MHz to 5.5&nbsp;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&nbsp;kbit/s data channel. 
* One 704&nbsp;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 code|polynomial]] is: <math>x^9 + x^4 + 1.</math>
* The pseudo-random generator is initialized with: <math>111111111.</math>

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 problems ===

<!--  Commented out: [[Image:NICAM-spectrum-PAL B G.png|600px]] -->

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&nbsp;kHz.
* The upper frequency limit of a NICAM sound channel is 15&nbsp;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]]s are all zeros, these bits can be discarded at no loss.
* On louder samples some of the [[least significant bit]]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&nbsp;dB with respect to the power of the vision carrier.
* The level of the FM mono sound carrier must be at least -13&nbsp;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 [dBμV]
# L(Measured) = measured level of the NICAM carrier [dBμV]
# R = -3&nbsp;dB bandwidth of the signal [kHz]
# BWAnalyser = bandwidth of the spectrum analyser [kHz]
# K = logarithmic form factor of the spectrum analyser ~2&nbsp;dB

note: if BWAnalyser is greater than R, the formula becomes L(NICAM) = L(Measured) + K

==Differing features==
NICAM sampling is not standard [[Pulse-code modulation|PCM]] sampling, as commonly employed with the [[Compact Disc]] or at the codec level in [[MP3]], [[Advanced Audio Coding|AAC]] or [[Ogg]] audio devices. NICAM sampling more closely resembles [[ADPCM|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,<ref name="AllYouEverWanted">{{cite web|url=http://stoneship.org.uk/~steve/nicam.html |title=All You Ever Wanted to Know About NICAM but were Afraid to Ask |author=Steve Hosgood |access-date=2007-08-30 |url-status=dead |archive-url=https://web.archive.org/web/20050214130459/http://stoneship.org.uk/~steve/nicam.html |archive-date=February 14, 2005 }}</ref> so that:
* <span style="font-family: monospace;">01111111111111</span> represents positive full-scale
* <span style="font-family: monospace;">10000000000000</span> represents negative full-scale

=== ±0 V has three binary representations ===
* <span style="font-family: monospace;">00000000000001</span> 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.
* <span style="font-family: monospace;">00000000000000</span> represents 0 V, with no +/- distinction
* <span style="font-family: monospace;">11111111111111</span> 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===
{{main|Videocassette recorder}}
[[VHS]] and [[Betamax]] home [[videocassette recorder]]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]] or NICAM TV) was [[frequency modulation|frequency modulated]] and then recorded, in addition to the usual audio and video VCR tracks, using the same [[Bandwidth (signal processing)|high-bandwidth]] [[helical scan]]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]] 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]]s due to their superior frequency range and flat [[frequency response]].

===DVD===
While recording in video mode (compatible with [[DVD-Video]]), most [[DVD recorder]]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]]
*[[Sound-in-Syncs]]
*[[VIMCAS]]
*[[Zweikanalton]] A2

== References ==
<references/>

==Further reading==
* Osborne, D.W. and Croll, M.G. (1973), [http://www.bbc.co.uk/rd/publications/rdreport_1973_41 ''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), [http://www.bbc.co.uk/rd/publications/rdreport_1973_42  ''Digital sound signals: Multiplexing six high-quality sound channels for transmission at a bit-rate of 2.048&nbsp;Mbit/s''.] BBC Research Department Report 1973/42.
* Reid, D.F. and Croll, M.G. (1974), [http://www.bbc.co.uk/rd/publications/rdreport_1974_24 ''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), [http://www.bbc.co.uk/rd/publications/rdreport_1977_38 ''Experimental 704&nbsp;kbit/s multiplex equipment for two 15&nbsp;kHz sound channels''.] BBC Research Department Report 1977/38.
* Kalloway, M.J. (1978), [http://www.bbc.co.uk/rd/publications/rdreport_1978_15 ''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
* [https://web.archive.org/web/20050214130459/http://stoneship.org.uk/~steve/nicam.html A technical description of NICAM]
* [https://web.archive.org/web/20120313020754/http://www.bbc.co.uk/reception/analoguetv/nicam.shtml The BBC's information page on NICAM]
* [https://web.archive.org/web/20101205071827/http://www.ee.surrey.ac.uk/Contrib/WorldTV/broadcast.html Overview of Television Broadcasting Systems]
* [http://www.mathworks.com/matlabcentral/fileexchange/41913 MATLAB NICAM function]

{{Video formats}}
{{Analogue TV transmitter topics}}

[[Category:Audio codecs]]
[[Category:BBC Research & Development]]
[[Category:Broadcast engineering]]
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[[Category:Television technology]]
[[Category:Television transmission standards]]
[[Category:British inventions]]
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[[Category:1986 introductions]]
[[Category:1991 introductions]]
[[Category:Audiovisual introductions in 1991]]