Newton-John guest judge for American Idol auditions

Olivia Newton-John

Olivia Newton-John spent her birthday this week as a guest judge for American Idol auditions and came away impressed by the singers.

"Some of them are very young and they're green but you can see their potential," she said. "They have a different voice or a different way of presenting themselves."

Other celebrity judges will include Jewel and songwriter Carole Bayer Sager.