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.

The idea was first described in 1964. In this, the 'ranging' was to be applied to the analogue signal before the

• A
  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

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

It has been standardized as ETS EN 300 163.[7]

Several European countries had implemented NICAM with the PAL and SECAM TV systems^[8][9][10]

• 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)
• ET1
  - historical, switched to DVB-T)
• Hungary (historical, switched to DVB-T)
• Iceland (historical, switched to DVB-T)
• 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 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
    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 31 October 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.
• 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 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.

No consumer grade equipment capable of NICAM modulation is presently known.^[11] Below is a non-exhaustive list of broadcast grade equipment capable of NICAM coding and or modulation:

• Philips PM5685/PM5686/PM5686A^[12]
• Philips PM5687^[13]
• Eiden 198A^[14]
• Pye/Varian/BBC Sound-in-Syncs solution^[15]
• IBA/RE Communications Sound-in-Syncs solution^[16]
• Tektronix 728E^[17]
• Rohde & Schwarz SBUF-E NICAM Module^[18]
• Barco NE-728^[19]
• CableWorld CW-3830

In order to provide

• The topology of this pseudo-random generator yields a bitstream with a repetition period of 511 bits.
• The pseudo-random generator's polynomial is: ${\displaystyle x^{9}+x^{4}+1.}$
• The pseudo-random generator is initialized with: ${\displaystyle 111111111.}$

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.

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.

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 sampling is not standard

The two's complement method of signing the samples is used,^[20] so that:

• 01111111111111 represents positive full-scale
• 10000000000000 represents negative full-scale

• 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

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.

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.

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

• Multichannel Television Sound
• Sound-in-Syncs
• VIMCAS
• Zweikanalton A2

• 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.

Related websites or technical explanations

• A technical description of NICAM
• The BBC's information page on NICAM
• Overview of Television Broadcasting Systems
• MATLAB NICAM function