Country singers Faith Hill and Tim McGraw are joining NBC's "The Voice" as key advisers. NBC made the announcement about the married superstars on Tuesday night. Tim and Faith will give advice and tips to Team Miley Cyrus, Team Adam Levine, Team Alicia Keys, and Team Blake Shelton. In a statement, Faith said, "I think having the perspective of performing live in many different venues, from clubs to stadiums, will help us in working with 'The Voice' artists this season.?