I never heard Callas live. My parents liked Tebaldi more than Callas and we had a collection of Tebaldi's operas on London (mostly mono). Callas was the great singing actress or acting singer. Near the beginning of the stereo era, she lost a lot of weight and much of the beauty of her voice. A good comparison is listening to her two EMI (Angel) Toscas. The first one in mono (IIRC from 1953) has her in prime voice, while the latter in stereo shows her decline. What is most difficult for me to listen to in her later recordings is her ever increasing vibrato, which turned into a wide wobble. She did rerecord several of her major roles in stereo, so finding the earlier mono usually has her in better voice.
EMI transferred all of their Callas recordings to digital (IIRC 24 bit/96Hz hirez) and they at least at one time were bargain priced. I bought the set of downloads a few years ago. The great dramatic Italian operas are where her acting/singing skills shine, usually paired with some of the top tenors of the day.
I may have told this story before. When I started grad school at Berkeley in the summer of 1967, one of the other grad students was a big opera fan. She found that I was also interested in opera. So in September, when she had a conflict, she gave me her ticket to see La Boheme at the SF . Opera. I had grown up listening to Boheme and other Italian operas at home (Sundays we listened to opera instead of church). So I went. I had heard of the Mimi, Mirella Freni, but not the Rudolfo. When the opera ended I remember thinking that this tenor was very, very good. This was Pavarotti's American debut.
When I wrote my Decca book, two of the engineers told me many stories about Pavarotti, who was a lifelong Decca artist. Of course, over his career, he did the opposite of Callas, gaining weight, until he could barely move across the stage. See his performances at the Met (
www.metopera.org) and notice the difference between Pavarotti in 1978 (the earliest Live at the Met videos they have) and the late 80's and earlyu 90's. He probably is 100 pounds heavier in the later performances.
Larry