Merrill Garbus heads up tUnE-yArDs, a four-piece project that defies genre: it’s pop, it’s rock, it’s funk, it’s jazz. Garbus, a former puppeteer, uses foot pedals to loop her voice and percussion during shows. The group’s latest album, “Nikki Nack,” made a big splash when it landed this spring, though the band’s been making records since ’09. They perform Sunday and Monday nights at Webster Hall.