🚀 go-pugleaf

> Richard, I know for a fact that ITT Semiconductor sells the chips for
> Nicam audio.I belive this stands for Near Instantaneous Companding.If
> you don't have an address I know I have it at work.Fax me your number
> and I will fax you the data sheet I have.My fax number is 415-967-0772
> 
> 
> 	Regards
> 	Norman Gillaspie
> 	ISS Engineering

Norman,

Well, thanks, but it wasn't me that asked! - it was Chris Allen
(chris@tharr.UUCP)...

NICAM == Near-Instantaneous Companded Audio Multiplexing, I believe :-).
Here's my understanding, cobbled together from the marketing FUD & the
data sheets etc. that I've seen (+ some guesswork, marked [*]).  Anyone want to
correct my understanding?

Multiplexing, because two audio channels and one control channel have to be
put onto one data stream.

Audio, for obvious reasons. [*!]

Companded, because there isn't a linear relation between digital quantisation
step and its analog[ue] equivalent. [*]

Near-Instantaneous, because the multiplexing implies a finite lag between
the audio data being put onto the stream and the conversion to analogue
form of those data.

Invented by the BBC.  Paradoxical how the BBC aren't advertising the fact that
they are transmitting programmes now in NICAM, although the Independent
networks are shouting loudly about it.  Perhaps this is because the Beeb
want to wait until most of the country's transmitters are NICAM-capable?

The control channel is there to tell the receiver what sort of data these are,
e.g. Stereo or two-channel bi-lingual (try doing that with sub-carrier FM!).
There is some redundancy in the control bandwidth, to allow for extensions
to the standard later, just as the BBC added into the Teletext standard,
when they invented that. [sound of richi's chest puffing out in nationalistic,
almost, but not quite, xenophobic pride.]

The audio data are 14-bit, but becuase of the companding, the dynamic range
is "comparable to CD" (at least on 99% of your average TV audio material).

richi.