it's a frequency designed to be heard not by the human ear, but by acoustic listeners. those acoustic listeners will then provide both a visual reference point, a wave form, and an audio sound which can be heard then by the ear. the pinger is not only designed for the 37.5, but the rhythmic one-second pings. there's many noises in the ocean. some of them are mammal made. others could be from other machinery. the sound -- we learned last night and over the last few days sound travels far, especially if it gets into the deep sea sound channel. but the pinger, the very noise of the pinger is designed to be unique. it is designed to be identifiable, and that is why angus houston said last night he was encouraged because it had the characteristics of the black