From wikipedia:
The bull was made entirely of bronze, hollow, with a door in one side... The condemned were locked in the device, and a fire was set under it, heating the metal until the person inside roasted to death.
The head of the bull was designed with a complex system of tubes and stops so that the prisoner's screams were converted into sounds like the bellowing of an infuriated bull. Perillos said to Phalaris: "[His screams] will come to you through the pipes as the tenderest, most pathetic, most melodious of bellowings." Disgusted by these words, Phalaris ordered its horn sound system to be tested on Perillos himself.
It sounds like fiction. How likely is it that the brazen bull is apocryphal? Or at least the part about playing the victim's screams like a musical instrument?
Are there any good sources I could read online maybe? I have looked and found none, but I don't know where to look.
Edit: added wiki link.
We don't really know whether Phalaris' bull really existed, although there's no shortage of textual references to it. Phalaris sort of became typical in classical literature of the excesses of the tyrants of the Archaic Period, and the story of the bull is explicitly used as a sort of parable about the cruelty of autocratic rulers in our texts. It's a frequent addition in philosophical and moralistic discussions--Cicero famously compared Verres to Phalaris and made an amusing joke at the expense of the Epicureans in the In Pisonem by asserting that Epicurus taught that the Epicurean should not be bothered by being in the bull of Phalaris. Diodorus interestingly places all responsibility for the bull on Perilaus (not sure why wikipedia seems to think his name is Perillos, all the sources I know of call him Περίλαος), who is punished by Phalaris for creating such a horrible device (I believe he's using Lucian as his source, who tells the story in the same way). It's nearly impossible to tell how much of this story is true and how much is just moralistic fantasy, as the truth of the story seems to be inextricably intertwined with the philosophical qualities that the story came to exemplify, but there's probably some grain of truth in it somewhere. Pindar is our earliest source for Phalaris' bull, and only a few decades after Phalaris' death he treats the story as if it's well-known and obvious to everybody. What exactly that's supposed to mean is a bit unclear--possibly Phalaris' cruelty (real or imagined) was combined with some imagery or motifs common to Acragas, where there were bull cults. But there's really not very much evidence to back this up. Further complicating the matter is the fact that it was at least believed that there really was such a bull that survived Phalaris' death. Cicero mentions that Scipio Aemilianus restored the bull to Acragas after it had been removed to Carthage. Whether this was the actual bull in question is pretty debatable, but there's a lot of uncertainty in the story that really can't be resolved--we simply don't know how true it is