SARAH JAROSZ Warmly old-school yet brimming with contemporary youthfulness, Jarosz melds bluegrass and folk, even some world rhythms, into a heady take on American roots music. Adept on acoustic guitar as she is on mandolin and banjo, she honed her chops at Boston’s New England Conservatory, where she studied contemporary improvisation. Add that to her blossoming songwriting and you’ve got a potent voice in roots music, whether composed or improvised. Her second recording, last year’s Follow Me Down, flows gently yet packs a sweet punch. With Ian Thomas. $12-$15. Neighborhood Theatre. Neighborhood Theatre.