Julien Ehrlich and Max Kakacek could hear the staggering differences in the songs they were writing for their third album as Whitney, SPARK—the buoyant drum loops, the effortless falsetto hooks, the coruscant keyboard lines. They suddenly sounded like a band reimagined, their once-ramshackle folk-pop now brimming with unprecedented gusto and sheen. But could they see it, too?

So in the ad hoc studio the Chicago duo built in the living room of their rented Portland bungalow, a shared 2020 escape hatch amid breakups and lockdowns, Julien and Max decided to find out. Somewhere between midnight and dawn every night, their brains refracted by the late hour and light psychedelics, they’d play their latest creations while a hardware store disco ball spun overhead and slowed-d...