It's an iconic scene in every dinosaur movie: the huge, conquering carnivorous theropod rears back and lets out a terrifying bellow. But how close to reality are these sounds? Do we have any ways of using science to figure out what dinosaurs and other stem-birds may have sounded like? Do we have evidence that they made sounds at all?
Sound effects artists spend huge amounts of time sampling vocalizations from various animals to create just the right mix to create an unfamiliar, otherworldly roar. Take a look at this Vulture article. It lists some of the amazing places sound effects artists went to create the sounds for the dinosaur movie Jurassic Park in 1993. The iconic T. rex roar was created by playing with the speed and frequency of elephant and dog sounds. The raptor sounds were created using tortoises, horses, and geese. Only one of these sources – the goose – is an animal anywhere close to being related to dinosaurs. Many of the other sounds are re-mixed from various mammals, the kinds of sounds we expect large predators (which today are almost all mammalian) to have, thus increasing the scare factor for audiences.