Next week sees the release of the self-titled final album by the British artist and producer Sophie, who died in 2021, aged 34, after an accidental fall. In the years prior to her death, Sophie had gone from underground darling to genuine alt-pop star, thanks to her ability to fuse, through generational talent and sheer will, the immediacy of pop with a futuristic vision of experimental music. When she died unexpectedly, slipping while trying to gain a better view of a full moon, tributes poured in across the musical spectrum, from Rihanna and Vince Staples to Arca and Flying Lotus – a breadth of adulation that could only have been earned by someone who had touched the mainstream and the underground.

Posthumous albums are a dime a dozen, and often cash-grabs by opportunistic labels or management teams, but Sophie is, at least to some degree, a complete statement. It’s a bittersweet final transmission from an artist whose textured, avant garde style had an outsized impact on the way pop sounds today – her epochal Charli xcx collaboration Vroom Vroom led to an era of pop that was faster, louder, sexier and sillier than before. Sophie’s work with Charli totally reinvigorated the latter’s career, turning her into an underground favourite and priming her to vault back into the mainstream with this year’s Brat. That record, which defined the summer, features two tributes to Sophie: the line “I wanna dance to Sophie” on Club Classics, and the song So I, about Charli’s complicated, distanced relationship with the producer.

Sophie, the album, was completed after her death by Ben Long, Sophie’s brother and longtime studio engineer. Speaking from Los Angeles, Ben says that he and his siblings, Emily Long and Katy Grimston, did not take lightly the task of completing their sister’s final record. Present in nearly all of Sophie’s studio sessions in the final few years of her life, Ben already knew intimately how the album would look when his sister died. The 16-song tracklist, which traverses pop, ambient music and techno, had been roughly sketched out by Sophie, and for many of the songs “everything was there – the arrangement, the production”. According to Ben, some songs only needed a little bit of mixing and mastering; others were between sketches and demos, but he and Sophie had discussed them at length, meaning he knew in which direction they needed to be taken.

The resulting album features longtime Sophie collaborators such as Cecile Believe, Hannah Diamond, Juliana Huxtable and Doss, and showcases the late musician’s interest in supremely challenging electronic music and euphoric pop. Intro (The Full Horror) is a soundscape built from ominous synth drones; The Dome’s Protection, featuring techno DJ Nina Kraviz, is an ambient, spoken-word song that feels clammy and alienating. In true Sophie fashion, the album is dense and unpredictable, never settling into the easy rhythms of a post-death tribute.

Many of the tracks were born out of parties where Sophie would produce music live, just so her friends had something to dance to. “She loved creating, but she didn’t do it much on her own,” says Ben. “She fed off other people having fun, and making people dance. It wouldn’t have interested her as much the following day to [pick up work on] the same songs. This is why she was so prolific – it was always next thing, next thing.”

Sophie was born and raised in England, the second-oldest of four siblings. It is commonly reported that Sophie and her family were Scottish; although Ben, the second youngest, says the family “do have a Scottish connection”, their father having been born there, he and his siblings stop short of confirming where they actually grew up, as Sophie often obfuscated details like this. “We don’t want to feel like we’re not doing what she would want,” says Emily, the youngest Long sibling. “She wanted to reach as many people as possible, and that idea of universality is sort of tied in with her not wanting to be defined so rigidly.”

Katy, the eldest, says she “can’t remember a time” when Sophie and Ben weren’t obsessed with music – particularly music that most other kids weren’t necessarily into quite yet. Before they were 10, the pair were being taken to music festivals by their father, where they would see artists such as the Chemical Brothers perform sets early in their careers. The Prodigy and Pet Shop Boys were two of Sophie’s favourites, and she gravitated towards Liam Howlett and Chris Lowe – the bands’ respective straight men, twiddling knobs in the background – rather than their charismatic frontmen. “Someone managed to get us a signed poster of the Prodigy, and it was of Keith,” recalls Katy. “I seem to remember her being a bit disappointed Liam wasn’t on it.”

Even in early childhood, Sophie was interested in making music, and her father would often take her and Ben to look at synths in instrument shops. One day, a friend of their dad gave Sophie an old synth, and she began experimenting, sampling sounds around the house and recording music. “I remember one time, she made my mum call up a friend who had a really squeaky voice, and she recorded it,” says Katy. “If someone said some sentence that was a bit silly or funny, she would turn it into a song.”

Sophie never outwardly articulated that she wanted to make music a career. “For her, it was always about: ‘Can I make something that sounds great?’” says Ben. Still, her interest in it never wavered. When she was a teenager, she began to DJ, and she and Ben would go out clubbing. Although they wouldn’t go exclusively to queer nights, Sophie gravitated towards spots that didn’t fit the typical “male, serious” dance music stereotype. “Something very macho, she wouldn’t feel comfortable in that,” says Emily.

After Sophie left home to attend art school, Ben says the big difference was “the amount of time she had. She didn’t have to worry about school, so that was when she started doing music all the time in her room, putting on parties.”

“It seemed a pretty steady progression in terms of making a career of it,” says Emily. “I remember one sound, [she] played it 10,000 times in a day in our house to try and get it right. To my ear, it sounded the same every single time, but she was changing it and perfecting it.”

Around 2009, Sophie moved to Berlin for a year to study. Marcella Dusi, Sophie’s ex-girlfriend, who performs on one Sophie track, Sfire1, remembers meeting Sophie in a club, and her having “a shy laugh, a very mysterious demeanour, charming and extremely beautiful”. When Sophie and Dusi lived together, Sophie still loved 80s bands such as Pet Shop Boys and New Order, but her taste had expanded to include avant garde musicians Sun Ra, Autechre and Moondog.

Although Dusi wasn’t a musician, Sophie encouraged her to try her hand at it, and the pair started a group called Motherland with their friends Matthew and Sabine. “I don’t remember the inspiration behind Motherland,” says Dusi. “It was Berlin at the height of indie sleaze, so you can imagine how most of our nights and days were going.” Jeffrey Sfire, who started making 80s-inspired dance music with Sophie as Sfire about that time, remembers being amazed on seeing Motherland perform at an art gallery. “I was listening to the riffs [and] I was like: ‘Woah, these are Prince-quality,’” he recalls. “That was my first impression of Sophie – this person’s a genius.”

When Sophie moved back to London, she began playing live sets. Andrew Thomson, founder of Glasgow label Huntleys + Palmers, remembers playing a bill with her at east London’s XOYO venue in 2010. “Very intrigued” by the music, he asked if she would remix a song for his new label, and later booked her to play a party on a beach in Barcelona the year after. “She ended up playing twice, with everyone going crazy for this new artist they’d never heard of,” he says.

In 2013, Thomson released Sophie’s debut single, Nothing More to Say/Eeehhh. Later that year on Numbers, another Glasgow label, Sophie released Bipp – a bulbous, euphoric track that seemed to do away with all pop and dance music convention and still wound up a total earworm. The song is now seen as a defining moment in 2010s pop; for Sophie’s siblings, it was just another Monday. “It was like: of course I haven’t heard this before, but it’s going to be really big,” says Emily. “I was prepared that it was going to sound new.”

In the intervening years, Sophie would release Product, a collection of singles that included Bipp and Lemonade, a camp, off-kilter track that was licensed for a McDonald’s commercial; forge enduring collaborations with artists such as AG Cook and Charli xcx; and be enlisted by pop musicians Madonna and Cashmere Cat for collaborations. She also experimented memorably with form and marketing, bundling some copies of Product with a silicone sex toy and creating a new project, QT, with Cook and performance artist Hayden Dunham, which was marketed as an eponymous energy drink.

In 2017, Sophie released It’s Okay to Cry, the first single from Oil, and used the video to announce to the world that she was transgender. Oil and It’s Okay to Cry represented a fulcrum in Sophie’s career: she had never been so vulnerable or personal in music before. “Sophie had done a lot of performing, she’d been out in the world for a long time, but in terms of her new identity, it was a big opening up in that record,” says Martha Brown, AKA Banoffee, a friend and collaborator. “It’s Okay to Cry was a really nerve-racking thing for her.”

“I can’t imagine her making a statement outside of the music, because it was the only place she really was public,” says Emily. “There was joy for her in that period, and she felt so accepted by so many people. I think we [siblings] all connected on a different level as well – just to bring us in felt really special and must have taken a lot for her.”

Brown, with Believe, sings the hook on Immaterial, Oil’s pop centrepiece and the defining song of Sophie’s career. They remember how offhand the session for that song felt, despite its huge impact. “We were hanging out and listening to each other’s demos. Sophie had started singing on tracks, which was super-exciting, but she said she didn’t think she could sing this song,” so asked Brown to try. “Sophie had a very specific idea of not only exactly what the melodies were and where they were placed, but the pronunciation of each word. I think I must have sung it like 100 times. I remember thinking: ‘This is a test, and I’m failing.’”

After Oil was released, Sophie began overhauling the way she made music, switching DAW – digital audio workstation, the app a producer uses to arrange and record – from Logic to Ableton. (“It’s a really huge deal,” says Believe. “It’s like a concert pianist being like: ‘I want to learn the cello.’”) She wanted, says Ben, to find a new way of working in which there wasn’t “much difference between studio, live show and release”, which would allow her records to capture the grit and fluidity of the way she made music in the moment.

Hence the album Sophie, which flows through and was designed to work in tandem with a live show she had been working on. Many of the record sessions sprang, without plan, from social events. One such song was Love Me Off Earth, the album’s final track and a collaboration with New York producer Doss, writer Thora Siemsen and artist M Zavos-Costales. Sophie and Ben were two of the last to arrive at Siemsen’s birthday party in 2018, and Sophie bonded with Zavos-Costales through discussions about poetry and art. Sophie invited the pair to the studio the next day, where she “gave us some time to free-associate” lyrics, says Siemsen.

“That play element was a big part of it,” says Zavos-Costales. “It’s easy to get caught up on a line or a verse, and if there was any moment where we felt a bit stuck, it was like: ‘This isn’t working right now, let’s focus on something else and come back to it.’” Love Me Off Earth, like Immaterial, is one of Sophie’s most transcendent pop tracks: loud, invigorating and skyward-soaring, in the way much of her best music is. “I want anyone listening to it to think about the sources of love they do have on this planet,” says Siemsen. “My main hope is that people dance to it at the club, that they listen to it in the car. I think it’s cathartic.”

Other songs, such as the Diamond collaboration Always and Forever, and My Forever, a song with Believe, prioritise sweetness and more classically pop melodies than Sophie often played with. “She’d messaged me and was like: ‘I’ve been really missing you and I was thinking about how one day it’d be really cool to write a song kind of like Electric Dreams,’” says Diamond.

My Forever also harks back to Sophie’s 80s obsession, specifically her love of Pet Shop Boys. “We were in the studio till the sun came up, basically,” says Believe. “We made it and then spent three or four hours just listening to it on loop – we knew we had made something that was such an emotional sweet spot.”

While Sophie, the album, was relatively fleshed out, her friends, family and collaborators say that Sophie was often circumspect about where she might have wanted to go next. This record, filled with best friends and born out of parties and formless hangouts, might be a perfect final chapter. “Sophie could see every card you’d ever played in your entire life, but you had no idea what hers were half the time,” says Brown. “She liked it that way.”

Sophie is released via Transgressive / Future Classic on 27 September.