After a 13-year radio silence, of course, the first question on many minds will be, What’s changed? The answer remains, as usual: not much. The duo has not significantly altered its formula since Music Has the Right to Children , though that’s not to say its discography has delivered diminishing returns; one of Boards of Canada’s talents has always been the ability to eke out subtle variations from a relatively fixed pool of sounds and moods. Geogaddi doubled down on Music Has the Right to Children ’s mix of lacerating hip-hop beats and woozy psychedelia; flush with acoustic guitars, 2005’s The Campfire Headphase carved out space for pastoral contemplation; things turned darker and muggier with 2013’s drone-heavy Tomorrow’s Harvest , their last album until now.…