The original 1963 recording of the Doctor Who theme music is widely regarded as a significant and innovative piece of electronic music, recorded well before the availability of commercial synthesisers.
Delia Derbyshire (assisted by Dick Mills) of the BBC Radiophonic Workshop used musique concrète techniques to realise a score written by composer Ron Grainer.
Each note was individually created by cutting, splicing, speeding up and slowing down segments of analogue tape containing recordings of a single plucked string, white noise, and the simple harmonic waveforms of test-tone oscillators which were used for calibrating equipment and rooms, not creating music.
The main, pulsing bassline rhythm was created from a recording of a single plucked string, played over and over again in different patterns created by splicing copies of the sound, with different pitches and notes achieved by playing the sample in different speeds.
Read more here (wikipedia)