This is actually two moments – or, two versions of the same moment! In any case, here are Tucker and Tebaldi singing, in god-like fashion, the final duet from Giordano’s masterpiece, Andrea Chénier. First, from the Ed Sullivan Show (March, 1957):
And next, from a stunning live performance from Chicago a year prior:
Singing of this quality has vanished from the face of the earth.