Tonight on its feature prime-time showcase The Essentials, TCM presents movies devoted to docudramas of famous singers. The evening opens with this 1980 musical biography of Loretta Lynn, starring Sissy Spacek as the eventual country music star, and Beverly D’Angelo as another, singer Patsy Cline. And pay close attention to Levon Helm, from Bob Dylan’s seminal backup group The Band, in a pivotal and complicated supporting role. Michael Apted directs, and is vey skilled at capturing the raw beauty of both the mountain environment and his leading lady. Spacek sings the songs herself, rather than having them dubbed in afterward.