"it is as though Verdi had decided to do something which he had been perfecting over the years, and to do it so beautifully that he need never to do it again. Formally, it is a step backward after Rigoletto". Budden describes one of the musical qualities as the relationship between the "consistent dramatic impetus" of the action being caused by the "propulsive quality" of the music which produces a "sense of continuous forward motion". Parker describes it as "sheer musical energy apparent in all the numbers". And Budden gives many examples which show Verdi as "the equal of Bellini" as a melodist. Verdi also clearly recognizes the importance of the role of Azucena. Remembering that the composer's initial suggestion to Cammarano was that he wanted to name the opera after her, Budden notes that this character "is the first of a glorious line" and he names Ulrica (from Ballo), Eboli (from Don Carlos), and Amneris (from Aida) as followers in the same vocal range and with the same expressive and distinct qualities which separate them from the other female role in the opera in which they feature. He quotes from a letter which Verdi wrote to Marianna Barbieri-Nini, the soprano who was due to sing the Leonora in Venice after the premiere, and who expressed reservations about her music. Here, Verdi emphasizes the importance of the role of Azucena: ..it's a principal, the principal role; finer and more dramatic and more original than the other. If I were a prima donna (a fine thing that would be!), I would always rather sing the part of the Gypsy in Il trovatore. From this position, Budden comments on the distinct differences in an era where vocal registers were less defined and which extend into Leonora's and Azucena's music "where greater verbal projection of the lower voice [can be] turned to advantage" and where "the polarity between the two female roles [extends] into every field of comparison." He then sums up the musical relationship which exists between the two female characters, the men having simply been defined as being representative of their own voice types, something evident and very striking in Verdi's significant use of voice types in Ernani of 1844. Regarding Leonora, Budden describes her music as "mov[ing] in long phrases most characterized by a soaring 'aspiring' quality" whereas "Azucena's melodies evolve in short, often commonplace phrases based on the repetition