UNDER THE RADAR: Even at a time when every startlingly talented new electronic producer seems younger than the one before, Australian wunderkind Harley Streten, who records and performs as Flume, might beat them all: he started with a music production program he found in his cereal box when he was 13 years old. Now 20, Flume has developed a sinuous sample-based, hook-heavy palette that won him a record store competition and a recording contract last year, not to mention a million-plus YouTube views and tours with the xx.