Budgies can register 150 images per second and hear sounds from 400 to 20 000 Hz. They have an amazing ability of storing sound sequences in their memory - this is why they can mimic human speech.
Humans can only register 16 images per second and they hear sounds from 16 to 20 000 Hz. Budgies have a more accurate sense of hearing, which allows them to distinguish certain signals very quickly - in the wild, this could mean life or death. This is why their hearing is in fact better developped than the general hearing of a human.