Some of the comments in this thread are pretty silly. Ironically, those who are talking about depth over flash are relying on a pretty superficial view of the matter:
I prefer emotions to mere sounds, so I'm not where you are and hope I never get there
Beauty over meaning. Gloss over substance. There is, of course, a certain irony about that in regards to Callas.
These are simplistic dichotomies, because beauty and meaning are
not independent things operating in isolation. A beautiful, pure pianissimo has a totally different effect than an ugly, shrill one. The "mere" sounds that singers make are what allow them to portray meanings. Expression comes through sounds. I'm not denying that ugly sounds are an important part of the repertoire of sounds for an opera singer. The problem with Callas is that her repertoire of sounds is deficient. She is frequently incapable of producing a high note without a serious wobble, which reduces the expressive range available to her. The excitement of a high note often comes from a quickening of the vibrato on that note. That effect, and many others, she cannot achieve. Now, I'm told that she makes up for these very fundamental and obvious flaws with great, almost mystical in some accounts, expression. Except, first, as I was just saying, I find her range of expression limited by her vocal flaws. But second, I just don't hear what is so unique in her interpretations. I don't hear musicality far in excess of any other singer, as I've often read claimed. I'm not saying she's unmusical. I'm just saying that I don't find her to be especially noteworthy in that regard. (If someone wishes to correct me, a thorough analysis of a specific part of a specific aria might help, but from experience I can say that throwing whole arias or operas at me and asking me to revel won't work.)
Additionally, voices, like all instruments, have natural expressive qualities. Flutes are purer than oboes, and oboes could never match their brilliance in this area, but the tart sound of an oboe likewise is an effect the flute can't achieve. The same is true of voices. The operatic voice has a particular range of expressive qualities, which do vary from singer to singer within limits, just as different violins of similar quality might have differences in timbre etc., that are unique, and to me, the most outstanding of any instrument. Just hearing a well produced operatic voice is a beautiful and emotionally powerful experience. There's nothing shallow or petty about it.
Some examples. Let's take the aria "Tu che le vanita." Callas did a famous version of this. The trick of this aria is in shifting moods of the text. The text opens with a declaration of the vanity of the world, and about escape from it in the grave. The words "mondo" and "profondo" are quite low, and clearly intended to be sung in chest voice (now I'm getting flashbacks to our discussion of Yannis Nezet-Seguin, but anyway.) But the thought turns to those who have holy pity in heaven, and to the lord himself. This part goes into the upper register, the sweet sound of which contrasts the bitter anger at the vanity of this world with the beauty and goodness of the next. The change in thought, providing characterization, is in the music itself. Now, so far this is all Verdi's genius. What the singer has to do to be properly expressive in this moment is have a strong, dark chest voice, and pure, beautiful top notes that can make this contrast. Let's listen to Callas and another singer.
Callas has the strong, dark chest register. Whatever my complaints about Callas, she usually had a good and thrilling lower register. But the top notes? The sound she makes on the word "cielo" at 3:10 is ironically infernal. It doesn't improve from there. It's shrill, and the forte top notes have bad vibrato. It isn't the pain of the character coming through, it's just painful. It's bad singing, full stop.
Selma Kurz, coloratura soprano, has both the strong, dark chest register and the pure, beautiful top notes to create the
contrast necessary to sing this aria expressively. The tone on the word "cielo" is positively gorgeous, a heavenly sound if there ever were one. It's not about me being some beauty junkie who just wants to bliss out and pretend there are no ugly sounds. Ugly sounds can be part a singer's expressive vocabulary. The problem is that for Callas they are not optional in far too many cases.
Let's take perhaps Callas' most famous role,
Norma. This is a very famous live performance from La Scala under Serafin in 1955. It's often lauded as her best performance. Now, let's take the central aria for the character of Norma, Casta diva. This aria is again, through Bellini's genius, masterful setting of a text. Norma is praying for peace, but with the hidden motive of her love for Pollione, the Roman soldier who might be killed in a war between the Druids and the Romans. Now, this text lies mostly in the middle and upper middle, and is made up of extremely long, beautiful lines. Callas does well with these lines, but whenever she reaches the upper middle, the wobble sets in (for example, on the word "inargenti"). Apart from being ugly, this makes her sound out of control of the sound, which makes me hear the
singer, Callas, and not the
character, Norma. This breaks me out of my disbelief, and makes it hard for me to get involved in the dramatic moment.
Now we come to the climax of the aria. Norma asks the moon to turn her beautiful face to us, "unclouded and unveiled". The music reaches its height on "sembiante" or "face". This is the face of the god Norma as priestess is there to adore and supplicate. This should be a moment of ecstasy. Her high note on 2:49 is awful. Wobbly and shrill. This spoils the moment entirely and adds nothing in recompense.
Now let's listen to Rosa Ponselle. First off, Ponselle never ever has the slightest hint of wobble. Second, I hear much about Callas's unique gifts in phrasing, yet as a purely musical matter, I much prefer the way Ponselle delivers Bellini's melody. Third, listen to the key phrase, "il bel sembiante." Whereas Callas gives us four equal notes at roughly the same volume, then goes for the shrill, wobbly top note, Ponselle varies the length and quality, at first shortening them, but making each successive note longer and more intense, until she suddenly attacks the last note softly, and the crescendos again, using that intensity to peak on a beautiful, perfectly controlled high note. Not only is it more interesting and individual as a musical interpretation, but the dramatic effect is sublime. It is as though she is imploring the moon, and suddenly sees what she is after. The ethereal beauty of her tone here is essential to the characterization: it is a reflection of what happens in her soul as she reaches this climax (pun intended - this is after all, a moment of both religious and sensual ecstasy). It is a beautiful and moment full of character and drama. I would take Ponselle over Callas every day of the week and twice on Sunday.
Now, I've been rather harsh for polemical purposes. I think Callas did a lot of good work, and early recordings are better than later ones. Certainly many great singers have flaws and have made unintentionally ugly sounds or let their instrument get away from them. Absolutely true. Even in those early Callas recordings, though, I often do not care for her middle and upper middle. That's too much bad voice for great singing. Ironically, my favorite recording of Callas is with her as Kundry in
Parsifal in 1949. But for me, her status as a mythical, unique genius who brought musicality and characterization unheard of previously in opera is ludicrous hyperbole. The idea that vocal beauty is a shallow add on to real depth is also a strange and rather perverse notion.