This article is from the MPEG FAQ, by Frank Gadegast phade@cs.tu-berlin.de with numerous contributions by others.
"NBC" stands for "non-backwards compatible". During the development
of the backwards compatible MPEG-2 standard, the experts encountered
some trouble with the compatibility matrix. The introduced quantisation
noise may become audible after dematrixing. Although some clever
strategies have been devised to overcome this problem, the question
remained how much better a non-compatible multichannel codec might
perform.
So ISO-MPEG decided to address that issue in a "NBC" working group -
among the proponents are AT&T, Dolby, Fraunhofer, IRT, Philips, and
Sony. Their work will lead to an addendum to the MPEG-2 standard
(13818-8).
 
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