SIERRA HULL An accomplished mandolin player at a young age, Hull already has a couple of solid recordings under her belt on the sturdy roots label Rounder records. Now, barely out of her teens, she’s honing her chops at Boston’s Berklee College of Music while recording and touring. Hull is a warm-voiced bluegrass singer/songwriter, a star in the making, and she can pick the mandolin like a veteran. (Samir Shukla)