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In article <26050001@hpopd.HP.COM> richi@hpopd.HP.COM (Richard Jennings) writes:
>/ hpopd:sci.electronics / chris@tharr.UUCP (Chris Allen) /  1:18 pm  Nov 14, 1990 /
>I have seen a number of adverts recently for Nicam Stereo televisions.
>Can anyone recommend any papers on the operation of Nicam Stereo?
>----------
>
>Don't expect many replies from the US, except perhaps "what's NICAM?", coz
>they use Luddite FM subcarrier analogue for their stereo TV (but, of
>course, they had it before we got it).
>
NICAM : Near Instantaneous CompAnding

	From what I remember, A section of the audio signal (something
	like 100ms) signal is digitised at 16bits, the most significant
	bits of the "loudest" sample are examined to determine
	how many bits to "shift left" each sample of the section of audio.
	The weighting factor is transmitted at the head of a "Packet" of
	data that consits of the most significant 10 bits of each sample
	that has been shifted left by the weighting factor. Sort of leading
	zero suppression.
	Knowledge of the whole 100ms of audio is needed before you compand
	and thus "near instantaneous".) 
	You end up with something like 10.2 bits per
	sample.
	Its a great idea that I think engineers ath the BBC
	came up with. It is not possible to transmitt the signal here
	in the US (or Australia) in the sameway its sent in the UK
	because the sound carrier is too close to the video here (4.5MHz
	in US and 5MHz in Australia but 6MHz in UK).

	(BTW the figures here are very rubbery but the method is right).

--
Michael Katzmann	NV3Z / VK2BEA / G4NYV
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Rusty Haddock		o  {uunet,att,rutgers}!mimsy.umd.edu!fe2o3!rusty
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