Not too long ago, you needed to carry around fairly big and heavy devices, like the walkman or the discman to listen to music on the go - not to mention the CDs and cassettes themselves. Thanks to the MP3 we live in a world where sound recordings and music only need virtual space. In our last video on the history of sound, Bretts tells you the story of the Compact Disc and how we got to digital sound data like MP3s.