An episode about singers, alone and in harmony. The latest installment of This Woman’s Work, a series from Classic Album Sundays and Studio 360 highlighting classic albums by female artists, focuses on “Lady Sings the Blues” by Billie Holiday, whose role as an innovator we are still coming to grasp. Kurt Andersen talks with composer Eric Whitacre about how his virtual choir is changing the game of choral music. And Aimee Mann explains how she wrote “Easy to Die,” about a friend’s overdose, for The Silver Lake Chorus, which commissions indie rock artists to write songs for them.