He's not usually in the spotlight. In fact, his task demands that he be as inconspiciuous as possible despite the fact that he's very tuned in and never misses a beat. Louis Yelnick is a page turner, and he's got the technique down to a finger-licking science. In places like Carnegie Hall or Avery Fisher Hall in New York City, he has turned the pages for the pianist who played for the violinist Itzhak Perlman. Mr. Yelnick describes his job as being "the man behind the man behind the man."