The landscape of the audience-ratings business began shifting with this morning’s announcement that Nielsen Holdings plans to buy Arbitron Inc. in a $1.62 billion all-cash deal. New York-based Nielsen will pay $48 per share under the sales agreement, a 26 percent premium from Maryland-based Arbitron’s closing price on Monday. The deal, announced Tuesday, is supported by the boards of both companies. Bloomberg News reports that the agreement will have to meet antitrust standards of the Federal Trade Commission before the sale can close. “I would expect to see some push back from local customers like local radio and TV operating groups,” Rich Tullo, an analyst at Albert Fried & Co.