this is what a castrato sounds like

https://www.youtube.com/watch?v=14MH2E94um4

(http://www.autoadmit.com/thread.php?thread_id=3970802&forum_id=2#36851051)

In the 1720s and 1730s, at the height of the craze for these voices, it has been estimated that upwards of 4,000 boys were castrated annually in the service of art.[11] Many came from poor homes and were castrated by their parents in the hope that their child might be successful and lift them from poverty (this was the case with Senesino). There are, though, records of some young boys asking to be operated on to preserve their voices (e.g. Caffarelli, who was from a wealthy family: his grandmother gave him the income from two vineyards to pay for his studies[12]). Caffarelli was also typical of many castrati in being famous for tantrums on and off-stage, and for amorous adventures with noble ladies.[13] Some, as described by Casanova, preferred gentlemen (noble or otherwise).[14] Only a small percentage of boys castrated to preserve their voices had successful careers on the operatic stage; the better "also-rans" sang in cathedral or church choirs, but because of their marked appearance and the ban on their marrying, there was little room for them in society outside a musical context.[15]

The castrati came in for a great amount of scurrilous and unkind abuse, and as their fame increased, so did the hatred of them. They were often castigated as malign creatures who lured men into homosexuality. There were homosexual castrati, as Casanova's accounts of 18th-century Italy bear witness. He mentions meeting an abbé whom he took for a girl in disguise, only later discovering that "she" was a famous castrato. In Rome in 1762 he attended a performance at which the prima donna was a castrato, "the favourite pathic" of Cardinal Borghese, who dined every evening with his protector. From his behaviour on stage "it was obvious that he hoped to inspire the love of those who liked him as a man, and probably would not have done so as a woman".[16]

(http://www.autoadmit.com/thread.php?thread_id=3970802&forum_id=2#36851121)

Modern castrati and similar voices

So-called "natural" or "endocrinological castrati" are born with hormonal anomalies, such as Klinefelter's syndrome and Kallmann's syndrome, or have undergone unusual physical or medical events during their early lives that reproduce the vocal effects of castration without being castrated. Basically, a male can retain his child voice if it never changes during puberty. The retained voice can be the treble voice shared by both sexes in childhood and is the same as boy soprano voice. But as evidence shows, many castratos, such as Senesino and Caffarelli, were actually altos (mezzosoprano) – not sopranos.

(http://www.autoadmit.com/thread.php?thread_id=3970802&forum_id=2#36851130)