I can't stop re listening to this. Both so wonderful but completely different. In the close quarters of the studio Dame Joan's voice is much bigger and rounder than Birgit's, but I think they would sound much different in a house. Apparently traffic made Joan arrive late and Birgit was not amused. One thinks of Sutherland's coloratura and high notes, but singing with the piano you realize the astonishing quality of Surtherland's middle voice. Nilsson does a jawdropping excerpt from Turandot. They are illustrating musical terms.