Cry to Heaven, Anne Rice
"He must know when to swell a note, how long to hold it, whether to break a passage into notes of unequal time or those of equal time, and how far he might go into ascending or descending intricacies. And he must at all times articulate the words of a cantata so that in spite of all this exquisite ornamentation, the meaning of the words was clear to everyone.
"'It was a fairly difficult novel to write,' Anne [Rice] said. 'It was a dare of sorts. I was trying to construct a story that was fundamentally extremely implausible, because no Venetian aristocrat had ever been made into a castrato. (...)
"She was limited by her ability to read Italian (...) The 'cry to heaven' is that of 'children mutilated to make a choir of seraphim, their song a cry to heaven that heaven did not hear.' The perfection of their voices, developed for religious purposes, is that even heaven should take notice, but at an expense no that no benevolent God should allow to happen. Yet God seems oblivious."
-Prism of the Night, Katherine Ramsland, pp. 198-9.