Humans can generally hear frequencies from 20 to 20,000 hertz. However, under ideal laboratory conditions, humans have been able to hear frequencies as low as 12 hertz. As humans get older or are exposed to loud sounds that damage their hearing, the highest frequency they can hear decreases.
Some animals can hear a much wider range of frequencies than humans can. Cats can hear frequencies from 55 to 79,000 hertz, higher than dogs and humans. Bats can hear an extremely large range of frequencies, between 1 and 200,000 hertz depending on the species, which makes up for their bad eyesight.