Some five years after buying media identifying service Gracenote for $260 million, Sony is selling it off to Chicago-based media company Tribune Co. for nearly half that. The two companies today announced a $170 million deal that gives the Tribune Companys Media Services group Gracenotes technology and database of 180 million music tracks and videos. Gracenote gets more than half a billion look-ups a day Gracenote says its database gets 550 million look-ups for media identification every day.