Canadian twin sisters Tegan and Sara Quin usually traffic in fizzy, punky pop music, so it's a refreshing twist to see them pop up at the 2011 Newport Folk Festival in Newport, R.I. The smart and outspoken pair will throw an extra curveball when they show their faces Saturday: They're translating their spiky music into acoustic arrangements. The mission is to highlight the sturdy songcraft behind Tegan and Sara's cultishly adored music, without sacrificing any of the hard-earned potency.