THE BBC has slapped demands for licence fees on all the companies selling Nicam digital stereo TV in Britain. The principles behind Nicam digital code are public, but the BBC holds an obscure patent that covers a vital feature of the system. Nicam converts stereo sound into digital code by sampling at 32 kilohertz, and describing each sample in a 14-bit word. By comparing each sample with the previous one, the words can then be scaled down to 10 bits. The BBC鈥檚 patent, UK 2 116 403, broadly claims 鈥渋mprovements relating to digital data transmission鈥� and covers error correction in any digital system. The idea is to save on digital bits by using some of them for two purposes.
The technique relies on the old idea of adding extra 鈥減arity鈥� bits to a digital data stream, and the receiver uses these bits to check for transmission errors. In the BBC patent, the parity bits also carry the vital information which tells a Nicam receiver how each 14-bit word has been scaled down to a 10-bit word.
The TV manufacturers鈥� trade body, the British Radio and Electronic Equipment Manufacturers鈥� Association, has already settled with the BBC on behalf of its members. Philips settled at the same time. The terms of the deals are confidential.
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The BBC is now gunning for the remaining companies. Korean giant LG Electronics is top of the hit list, with foreign factories that supply unbranded TVs for high street chains close behind.