Is this Caballé's greatest moment? Norma: "In mia man" duet w/ Jon Vickers @ Orange, 1974

(This video is uploaded for educational purposes only, and this channel does not monetize it.)
Commentary from me is superfluous. This is stellar singing and superb interpretation. For me it was Caballé's greatest triumph, and as far as Normas of the second half of the 20th century go, second only to Callas herself.
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Yes, the singing is... extra.
Trrill™ is about florid passages, improvisatory underpinnings, staccato'd intuitions, and virtuosities even at their most ridiculous.
But it's also about the biggest, boldest form of vocal emission, with aural examples of basically correct singing, correct impostazione-chiaroscuro, vowel clarity, firm and centered pitch, correct vibrato action, absence of throatiness or thickness, sounds free from constriction and from the acoustic noise that accompanies it-with occasional video examples that demonstrate what the body, face, mouth, jaw, and tongue look like when used with correct impostazione-the vocal emission of the one and only Italian school.
Caveat: I'm biased in favor of #baritones and baritone literature, but if you want to learn about and listen to all the greatest singers in the old-school tradition, explore this spreadsheet (voice parts are separated by tabs):
bit.ly/2W4qmE3