De Hidalgo later recalled Callas as "a phenomenon... She would listen to all my students, sopranos, mezzos, tenors... She could do it all." Callas herself said that she would go to "the co...

In 1968, Callas told Lord Harewood:

"De Hildalgo had the real great training, maybe even the last real training of the real bel canto . As a young girl—thirteen years old—I was immediately thrown into her arms, meaning that I learned the secrets, the ways of this bel canto...

Matthew Gurewitsch: "In fact the essence of her art was refinement. The term seems odd for a performer whose imagination and means of expression were so prodigious. She was eminently capable of the grand gesture; still, judging strictly from the evidence of her recordings, we kno...

"The tone of the voice was warm, lyrical, intense; it swirled and flared like a flame and filled the air with melodious reverberations like a carillon. It was by any standards an amazing phenomenon, or rather it was a great talent that needed control, technical training and strict discipline in o...