According to John Ardoin, however, these two singers should never have been compared. Tebaldi was trained by Carmen Melis, a noted verismo specialist, and she was rooted in the early 20th century Italian school of singing just as firmly as Callas was rooted in 19th century bel canto. Callas was a dramatic soprano, whereas Tebaldi considered herself essentially a lyric soprano. Callas and Tebaldi generally sang a different repertoire: in the early years of her career, Callas concentrated on the heavy dramatic soprano roles and later in her career on the bel canto repertoire, whereas Tebaldi concentrated on late Verdi and verismo roles, where her limited upper extension and her lack of a florid technique were not issues. They shared a few roles, including Tosca in Puccini's opera and "La Gioconda", which Tebaldi performed only late in her career.