Delia Ann Derbyshire entered the world on Wednesday 5 May 1937, two years before the Second World War broke out. She and her younger sister Benita (who died in childhood) were born in Coventry to devout Catholic working-class parents Emma (Emmie) and Edward (Ted) Derbyshire. The family home was 104 Cedars Avenue, clearly marked on the canister of Delia’s government-issue gas mask, a relic from her first eight years lived in the shadow of war. With all the disruptions that brought to everyday life, obeying orders was imperative. At times it could mean the difference between life and death. Maintaining daily routines and optimism for the future was vital for morale. Her upbringing was all about precision and order, secular and religious. The old mantras must have been drilled into her – cleanliness is next to godliness, a tidy house is a tidy mind, a place for everything and everything in its place. That included children. Parenting was nothing like now for Delia and myself. Our parents weren’t our ‘best friends’, children didn’t have lots of toys, and jumping on sofas or noisy play indoors wasn’t allowed. Physical games took place outside, and even then weren’t permitted to disrupt set routines, annoy neighbours or get out of hand. Bad behaviour wasn’t tolerated. So children grabbed opportunities and found places to let rip well out of sight of their parents. Children’s feelings were repressed too. Crying or those involuntary squeals of excitement I love to hear didn’t always meet with approval. I remember being told to stop crying, stop acting ‘up’, stop acting ‘out’, calm down or simply shut up and ‘behave’, or else …

Delia and I both had an aptitude for the arts and science. Delia’s first love was music and she started learning to play the piano at the age of eight, but the educational system viewed the arts as secondary to academic subjects. When she was eleven years old she started at Barr’s Hill High School for girls. One period a week was allocated for music, and that was for either singing or learning to play the violin – which she hated. Her request to switch to the piano was refused, so she took it upon herself to make sure she got what she needed and continued with private lessons, supported by her parents, who bought her a piano. By the time she was thirteen she’d reached a high level of proficiency, performing at festivals, entering and winning competitions, and joining the National Youth Orchestra. I never reached the same levels as Delia, but we shared a love of Beethoven’s sonatas, my favourite being ‘Für Elise’, one of very few pieces I would play voluntarily for my own pleasure. I was eleven when I took my first piano lessons. Our piano was against one wall of the dining room, next to the table where my mother would often sit after work, crunching numbers for the workers’ wages on a big Burroughs adding machine while I did my piano practice, her ‘playing’ the big adding machine, punching away at the keys, setting in motion the rhythmic kerchunks as the internal metal mechanisms did their reckoning. It was like a duet – mathematics in audio motion accompanied by my piano chords and occasional outbursts of expressive, informal, off-script whacking of random ivory and black keys.

Although much of Delia’s time was taken up with practising the piano, she had a boyfriend, Graham Harris. They had been born a few weeks apart and got to know one another through their parents’ friendship and frequent visits to his home. Their childhood affection changed to something deeper when Delia turned up to Graham’s sister’s birthday party looking like a goddess in her pale blue dress. Graham was smitten and the two fourteen-year-olds entered into a ‘love affair’, exchanging letters – with Delia’s always written on blue Basildon Bond and delivered to Graham by her friend Lois, who caught the same bus home as him. In the summer months they would meet up and play tennis together, then go for ice cream. Much to Graham’s delight, Delia would ride her bicycle to meet him outside the school gates. Even in her school uniform of blue-and-white-striped dress, navy blazer and straw boater she was captivating. Delia made such an impression on Graham, he carved her name in twelve-inch letters on a quarry wall when on a school trip.

Delia’s schooling instilled in her a rigorous approach to everything that affected her for the rest of her life, creating an obsession with accuracy. She used mathematics as a route to (near) perfection in her music. Yet, much like myself, she was resistant to certain rules from an early age. We shared a need to ‘get out’, not wanting to be swallowed up by the system and family pressures, an unwillingness to accept limitations that stood in the way of our own plans. I had no rigid plan but Delia did, and she knew what was important in order to fulfil her ambition of going to university, being involved with the arts and working at the BBC – where everyone spoke so ‘very very’ well. She needed to get the ‘fit’ right, and her Coventry accent would have flagged her as being from up North, which in snob circles would have had a negative effect on her status and credentials. She took elocution lessons and built on them to eradicate or at least conceal any traces of her accent – incorporating ‘golly gosh’ and ‘tickled pink’, among other typically polite quips, refashioning her voice into the very distinctive, rather posh one everyone knows her by. You could say her first sound project was her own voice.

Delia excelled at mathematics and unusually for a working-class girl was awarded a scholarship at Cambridge University, the most prestigious place for the study of mathematics. I was only five years old and starting school for the first time when Delia was enrolled at the all-female Girton College in 1956. She was over the moon but her elation didn’t last long. The misogynistic attitudes she experienced were bad enough to cause a third of her fellow students to drop out in the first year. Delia wasn’t going to give in. Ironically, so many women leaving the course presented her with an unexpected opportunity to switch subjects, from reading mathematics to music.

Having finally gained access to the place where she could increase her knowledge, she found the course boring. Much to the disapproval of her tutors she strayed away from the syllabus, which focused on the period 1650 to 1900, to investigate the theory of sound and a broader range of medieval and modern music. Delia had an open mind when it came to music: the term covered a very broad spectrum. For her it included the ancient and modern, physics, mathematics, harmonics and acoustics. She also knew music could be a free and adventurous creative field to work in, having had such a fun time abroad when she toured Europe providing sound effects for the Pembroke College Players’ performances of Julius Caesar.

Just before her graduation in 1959 Delia and her music student friend Jonathan Harvey (whom she’d first met when in the National Youth Orchestra) took a trip to Brussels to visit Expo ’58, the World’s Fair. They went specifically to see Le poème électronique at the Philips Pavilion, a symbol of post-war progress in technology, designed by Swiss–French architect Le Corbusier and Greek architect and composer Iannis Xenakis, with its light show and music by the French composer Edgard Varèse. It was so much more than a building. It was an experiential space that was itself the embodiment of the ‘poem’, as Le Corbusier was eager to point out: ‘I will not make a pavilion for you but an Electronic Poem and a vessel containing the poem; light, color image, rhythm and sound joined together in an organic synthesis.’ The building was dynamic and impressive, in the way people in the 1950s imagined the future would look – what we now refer to as retro-futurism. The structure was composed of nine hyperbolic paraboloids, resembling the shape of a 3D waveform similar to one generated by an oscilloscope.

Delia and Jonathan entered the pavilion to be greeted by an eight-minute, seven-part audiovisual show of projections and electronic music on the theme of the history of humankind. They sat on the floor of a stomach-shaped space, surrounded by walls and surfaces designed with mathematical precision relatable to the theme itself, and with a control tape that routed sound to 350 speakers. The whole audiovisual and physical effect of sitting on the floor and feeling the sound vibrating was an immersive experience and undoubtedly a huge influence on Delia. The meeting of geometry and sound must have been music to her ears. After the war people could once again afford to look to the future, and there in the Philips Pavilion was the future of visual art, music and mathematics in all its blazing glory, awaiting Delia’s ‘call’. By the time she’d left Cambridge the Philips Pavilion, which had likely helped to light the spark of her...