During "The Callas Debate", Italian critic Rodolfo Celletti stated, "The timbre of Callas's voice, considered purely as sound, was essentially ugly: it was a thick sound, which gave the impression of dryness, of aridity. It lacked those elements which, in a singer's jargon, are described as velvet and varnish... yet I really believe that part of her appeal was precisely due to this fact. Why? Because for all its natural lack of varnish, velvet and richness, this voice could acquire such distinctive colours and timbres as to be unforgettable." However, in his review of Callas's 1951 live recording of "I vespri siciliani", Ira Siff writes, "Accepted wisdom tells us that Callas possessed, even early on, a flawed voice, unattractive by conventional standards—an instrument that signaled from the beginning vocal problems to come. Yet listen to her entrance in this performance and one encounters a rich, spinning sound, ravishing by any standard, capable of delicate dynamic nuance. High notes are free of wobble, chest tones unforced, and the middle register displays none of the "bottled" quality that became more and more pronounced as Callas matured."