JACKSON, Miss.—“I have a song I want you to listen to,” Tommy Couch Sr. told Dorothy Moore over the phone in 1973. Putting down the receiver and stepping out of her great-grandmother’s house on Monument Street in Jackson, Moore walked to the nearby Malaco Records. Inside the studio, Couch sat at the soundboard, pressing play and letting music fill the studio with the sounds of “Misty Blue,” a slow, country tune about the struggle to get over a lost lover.