Imagine a world without the power to capture or transmit sound. Journey with Steven Johnson to the Arcy sur Cure caves in northern France, where he finds the first traces of the desire to record sound - 30,000 years ago. He also learns about the difference that radio made in the civil rights movement and reveals the Hollywood star who designed a WW2 weapon that would make possible the modern cell phone network. 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.

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Tags: PBS, How, Got, Now, 6of6