In this video from 1965, electronic music pioneer Delia Derbyshire, who arranged the original theme music for Doctor Who, demonstrates how electronic music was made at the BBC Radiophonic Workshop. It’s such a treat watching her construct songs from electronic sound generators and sampled sounds played at different speeds and pitches; you can even see her layering sounds on different tape machines and beat matching, just like DJs would years later.
Amazingly, you can try your hand at layering and looping this music yourself with this Tape Loops demo from the BBC. You can also make Dalek and Cybermen noises with the Ring Modulator, create Gunfire Effects, or use the Wobbulator (my favorite).
See also The Definitive Guide to Doctor Who Theme Music, the trailer for Delia Derbyshire: The Myths and the Legendary Tapes, and this incredible proto-techno track Derbyshire made in the 60s. (via @austinkleon)