New York debut at the Metropolitan Opera in February 1948 as the Duke of Mantua in Verdi's Rigoletto after singing the role in Riccione with Hjördis Schymberg in August of the previous year. After his performance in Manon a month later, Musical America wrote that Di Stefano "had the rich velvety sound we have seldom heard since the days of Gigli". He went on to perform regularly in New York for many years. In 1957, Di Stefano made his British debut at the Edinburgh Festival as Nemorino in L'elisir d'amore and his Royal Opera House, Covent Garden, debut in 1961, as Cavaradossi in Tosca. As a singer, Di Stefano was admired for his excellent diction, unique timbre, passionate delivery and, in particular, for the sweetness of his soft singing. In his Metropolitan Opera radio broadcast debut in Faust, he attacked the high C forte and then softened to a pianissimo. Sir Rudolf Bing said in his memoirs, "The most spectacular single moment in my observation year had come when I heard his diminuendo on the high C in "" in Faust: I shall never as long as I live forget the beauty of that sound". During his years of international celebrity, Di Stefano won a gold Orfeo, an Italian musical award. In 1953 Walter Legge, leader of EMI's classical wing, wanted a tenor to record all the popular Italian operas with Maria Callas, and chose Di Stefano. Among their recording achievements was the famous 1953 studio recording of Tosca under Victor de Sabata, which is considered "as being one of the great performances in the history of the gramophone". The two also performed together on stage frequently, from 1951 in South America to the end of 1957 in Un ballo in maschera at La Scala, the last time the two collaborated in an opera. He sang Alfredo in the famous Visconti production of La traviata in 1955 at La Scala, as well as Edgardo to her Lucia under Herbert von Karajan at La Scala, Berlin and Vienna. Rudolf Bing of the Metropolitan Opera House lamented Di Stefano's playboy lifestyle, which he felt was the cause of his vocal decline, although Di Stefano himself blamed allergies to synthetic fibres for permanently damaging his vocal cords. In 1973, Di Stefano and Maria Callas went together for a recital tour that ended in 1974: critics remarked that Maria Callas had lost her voice,