S1, E6: Imagine a world without the power to capture or transmit sound. Journey with Johnson to the Arcy sur Cure caves in northern France, where he finds the first traces of the desire to record sound — 10,000 years ago. He also learns about the difference that radio made in the civil rights movement and discovers that telephone inventor Alexander Graham Bell thought that the best use for his invention was long-distance jam sessions. During an ultrasound on a pregnant dolphin, he realizes just how big a role sound has played in medicine. The unsung heroes of sound have had an impact on our working lives, race relations, saving lives and the radical alteration of cities.