Editing NICAM (section)

=== 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]].