Some bands, with their interpersonal dynamic, give the impression of cold efficiency. Others seem to be just barely holding it all together. My Morning Jacket embodies a preferable third option: nothing but warmth, and a conviction that music-making still largely comes out of a hang. Last month I visited the band’s hometown of Louisville, Ky., on business, and plugged into their vibe firsthand. We talked a lot about Circuital, their intensely cohesive new album, and how it came to be.