When Polow da Don isolated those three bittersweet chords, pedaling between major and minor, he must’ve known. Those chords—taken from the extended intro to the 1979 smooth-soul jam “ I Call Your Name ,” by the Ohio-based band Switch—suggested both dawning joy and nagging worry, forward motion and hesitation. They don’t just move; they glide. They suggest dramatic entrances, receding horizons. They hint that something glorious might be over the next rise. He looped those three chords into four bars, inserting another hiccuping little loop in the middle. The result was a bottled hit of giddy anticipation: The beat to “Throw Some D’s” swoons grandly into view, then does so again, then does so again. Every time that third stair-step chord hits, new vistas open up, and we eagerly scan our environment for new information. During its four minutes, “Throw Some D’s” climbs that little three-chord staircase roughly 18 times, and Polow sends new sonic cartoon characters scurrying across the frame with each repetition.…