Sixteen years ago, the soundtrack to “O Brother, Where Art Thou,” produced by T-Bone Burnett, almost single-handedly caused a resurgence in the popularity of old-time bluegrass and mountain music. Rolling Stone recently ranked it No. 1 among all movie soundtracks. At the center was Dr. Ralph Stanley, who grew up in the Appalachian Mountains and was among the first generation of American bluegrass players. He was known for his clawhammer-style banjo picking and his distinctive voice, which “sounds like it’s coming out of the past, like a ghost or something,” said his biographer. Stanley died this week at age 89.