Wobble vs Vibrato

Posture. Interesting observation. Watch Callas in Germany in the 60's during those famous concerts. She collapses her shoulders inwards and even hunches her back. The sound is forced and strained. You can see she is singing with her throat, the veins standing out and the face terribly taught, as is the jaw. Entirely different on the recently discovered 1957 kinescope from the RAI studios where she sings Casta Diva. She is very slim by then, but stands erect, shoulders back, beautifully supported top notes. I am not sure that the weight loss was the problem.Cheers,Patrick Byrne