1. 
   AC3
   (audio) An audio format by Sony[?], the successor of AC2. AC3 is used for multi-channel audio for digital video. (2001-12-18)
   Found op http://foldoc.org/AC3
   
   
2. 
   AC3
   Audio Codec 3. This was the original and more technical name for Dolby Digital. Replaced by marketing mavens when they realized that Dolby's name was not in the title. Some RF modulated, 5.1-encoded laser discs were labeled as AC3. Later versions were labeled as Dolby Digital.
   Found op http://www.encyclo.co.uk/local/21058
   
   

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