Brad and Andrew Barr have been my favorite guitarist and drummer, respectively, since their time in New England trio the Slip. Now, with Sarah Page on harp and Andres Vial on keys, the Montreal quartet’s new set as the Barr Brothers, Sleeping Operator, arrives this fall. They’ve long pushed the envelope, unlocking genres from jazz to folk and world music, from psych-rock to at least one notable nod to classic rock. This outfit, though, is more bent on extending the traditional singer-songwriter palette. Case in point, new cut “Half Crazy” is described as an “offspring of the North African desert music of Mali/Morocco with the sweat and electricity of the Chicago and Mississippi Delta blues.” The result is a killer, off-kilter blues jam (dig the instrumental breakdown at 2:05). It’s best settled down by their own “Even the Darkness Has Arms”: