The Los Angeles Memorial Sports Arena is swarming with cops. SWAT team helicopters circle, squad cars fill the parking lot and medical tents are on standby. But they're not here because of the anti-establishment rock star lurking in the basement; this venue is also the centre for the LAPD rapid response units awaiting riots in reaction to the Trayvon Martin verdict.

"There was a little violence outside here," says Trent Reznor, enclosed in a darkened corner sanctum, scented with incense "to mask the smell of sewage". It's 11am, but the ambience is cigar lounge at dusk. "There were mild demonstrations that turned violent the first night. I'm not that worried about it, but it can't help but focus you in on some pretty inherent, severe problems." He gives a sardonic smile: "Welcome to America."

The cavernous lair beneath the arena is on lockdown too. For weeks it's been the secretive subterranean base for Reznor, the 30m-selling industrial rock icon behind Nine Inch Nails. As the band who have spent the last two decades forcing brutal – yet seditiously melodic – electronic hardcore and bleak ambient rock down the gullet of the mainstream, the chaos around them seems apt.

Reznor, after all, is not one for a quiet life. He's the guy who discovered, nurtured and dismissed Marilyn Manson; who recorded a noir-rock benchmark – 1994's 5m‑shifting The Downward Spiral – in the house where Sharon Tate was murdered; and who survived a heroin overdose in 2000 in the grip of one of rock's most pre-ordained self-destructions.

But today, having spent the last decade as a technological dambuster and champion of the new cyber-DIY generation, he is a respected and solemn elder statesman of the crueller end of alternative culture. He's the first person director David Fincher calls when he wants an Oscar-winning soundtrack (Reznor provided the score to The Social Network among other films) and Queens of the Stone Age main man Josh Homme rings when he needs to know how to bounce back from a near-death experience. And he's about to release NIN' minimal and reflective eighth album Hesitation Marks – the band's first since 2008's The Slip – which casts him as the classic scarred rock casualty snatched from the abyss by fatherhood and family.

"I was thinking a lot about The Downward Spiral album era, and the person I was at that time," he says, awkward, verbose but reasonably zen at 48, still clad in shredded black threads but a far more affable prospect than his intense and difficult reputation suggests. "Downward Spiral felt like I had an unending bottomless pit of rage and self-loathing inside me and I had to somehow challenge something or I'd explode. I thought I could get through by putting everything into my music, standing in front of an audience and screaming emotions at them from my guts ... but after a while it didn't sustain itself, and other things took over – drugs and alcohol."

He has mellowed significantly. "And I'm happy that I don't feel that way any more. I've learned to recognise, a lot of it forced through the process of recovery, that I'm wired wrong in certain ways, the chemical balance of my brain is off in terms of depression a little bit. This record was written as the other side of that journey. The despair and loneliness and rage and isolation and the not-fitting-in aspect that still is in me, but I can express that in a way that feels more appropriate to who I am now. And often that rage is quieter."

Reznor's reformed incarnation of NIN has spent weeks underneath the LA Sports Arena piecing together two live shows: one for an arena tour starting in the US in September and one for the festival circuit. These will be the first NIN shows since Reznor broke up the band following the Wave Goodbye tour of 2009. He did so to concentrate on composing the soundtrack for The Social Network and to start a family – not to mention a band called How to Destroy Angels – with his new wife Mariqueen Maandig.

And if the comeback alone doesn't ramp up expectations, consider that his 2008 Lights In The Sky tour was a technological marvel featuring an LED curtain across the front of the stage that framed the band in ruined cityscapes or shifting stockades of static, like Pink Floyd's wall plugged into The Matrix. When NIN rise from the dead, plug-in-and-play just won't do.

"I found that the explosion of the EDM movement and what those guys bring to their shows kind of pushed me the other way." he says. "The last thing I want to do is make a show that feels like a tech demo. 'Look what I bought!' This show's mostly about shadow and light."

The reason the NIN reunion is so feverishly anticipated in certain tech-rock dungeons is that Reznor is a master of the art of immersion. On his emergence with the 1989 debut Pretty Hate Machine and its standout single Head Like a Hole, this immersion was aesthetic. Snarling songs of bilious angst, Reznor – an ex-janitor and horror movie fanatic from Pennsylvania recording much of his music himself – displayed such fierce independence and cyberpunk allure that he offered fans a dark, passionate and consuming package to dedicate themselves to.

By 1994's breakthrough The Downward Spiral, it had become ideological, psychological and gruesomely morbid. He recorded the album in a studio called Le Pig that he'd built in the Hollywood Hills house where Tate was killed by the Manson Family, promoted it with torture-porn videos and was sucked so deep into its hour-long concept of a self-destructive protagonist inching towards suicide that he developed raging cocaine and alcohol addictions under the pressure of its success. Fact very nearly mirrored fiction: following a failed rehab attempt, while touring his soundscape epic The Fragile in 2000 Reznor overdosed in London on China white heroin that he had mistaken for cocaine.

"I was so deep in the throes of addiction that it was shitty, but it didn't seem that much shittier than a lot of other things, other surprises that kept happening," Reznor confides. "You tend to accumulate dramatic bad things when you're in that place. My house got broke into, how did that happen to me? Oh my car got stolen, oh I woke up in hospital … it doesn't sound that out of the ordinary when everything is shitty. For me, it was another brick in the wall of realising at some point, enough."

The freshly clean Reznor has instead spent the 21st century indulging his inner tech obsessive. He has explored the latest on-stage hardware and in-studio techniques and has been eager to use cyberspace to give his fans an all-encompassing multimedia experience. Its pinnacle was 2007's Year Zero project, an apocalyptic concept album about a futuristic US dystopia run by the military and populated by drug-controlled surveillance slaves. Initially, Year Zero sounded about as sci-fi as an Oyster card. Then fans began finding hidden website URLs imprinted into their promotional T-shirts and USB sticks of coded static left in toilets at NIN gigs. These clues led them to a labyrinth of websites for fictional organisations such as the Bureau of Morality and the First Evangelical Church of Plano, all part of an ultra-elaborate alternate reality game. For two months Year Zero lit up the web, turning from a cloak-and-dagger internet lark into a concerted effort to rally real-life political protest. Complete immersion.

Today, Reznor sees an America slipped way beyond Year Zero. "It was meant to be a cautionary 'Watch what's going to happen'," he says, "but it's kind of past that now. Watching Bush embarrass America [back then], things were changing at such a pace that it felt like they weren't even trying to hide it any more. Any trust you might have of the government, or the illusion that big business isn't running everything and really everything's a scam to conduct the brilliant manipulation of lots of uneducated people in America … that was gone."

His initial optimism about Obama seems to have evaporated, too. "The day he was elected really felt like: 'I can't believe that just happened.' Jump ahead a few years and … I know one person can't change everything and it's the system that's broken, but the [Edward] Snowden shit that we're finding out about now, is this a surprise to anybody? But no one will do anything about it. We just had banks rip us off, bankrupt the country. Who went to jail for that? Who's accountable for that? Whatever changed about that? Nothing. [Year Zero] has come true. And nobody's doing anything about it, nobody cares. Some people speak up, but only when convenient. Complaining about it on social media isn't gonna change anything."

As America spirals ever-downward, Reznor's descent has spectacularly reversed. While touring with How to Destroy Angels, he remembered he owed Interscope a NIN greatest hits. Keen to clear his debt, early in 2012 he set about penning two new songs for the collection, Satellite and Everything. "It felt fresh instead of a chore or a job," he says. "They felt like two different versions of where I might go if I were to start making a record. So I thought: 'Rather than piss these away on a greatest-hits record which nobody cares about, including me, why don't we see if there's an album in there?'"

A new solitary writing technique helped hammer home the new Nails sound. "What I found the most inspiring was sitting with just a drum machine in my bedroom, in my office," he says. "Not having a keyboard or a guitar and playing everything on pads. Me sitting alone with literally one piece of gear just messing around, I found it exciting. It lent to the minimal edge, because it didn't feel like it needed more."

If Hesitation Marks seemed to cohere from the ether, its performance proved tougher to realise. Early recruits to the new NIN line up included King Crimson's Adrian Belew and Eric Avery of Jane's Addiction. A few months in rehearsal and both were out, Belew claiming "it didn't work" and that Avery was "overwhelmed by the intensity that Nine Inch Nails demands".

"I hear that I'm a prick at times," Reznor says, "but I just want to do the best work I can do. Not unrealistic, but it's kinda unrealistic. Nine Inch Nails is like building an army to go conquer. We build it, then we play, and we have to play so much to validate building it, financially. It leads to getting burn-out because a tour that would be fun if it lasted three weeks has to last 15 weeks."

Contrarily the finished album – imagine an industrial cousin to Radiohead's In Rainbows that flips between glowering glitchtronica and whoomp-laden rock – suggests a Reznor mellowed with age. Now a stable and sober father to two young boys, Lazarus Echo and Balthazar, can he be considered ultimate proof to every worried parent that their troubled kid will eventually grow out of it? Reznor smiles. "It reminds me, when I was in the throes of that was when we toured with Bowie, and this was the Bowie that had come out the other side and was happily married. I was nearing the peak of my addiction, and his role to me was kind of mentor, big brother, friend, and also he'd give me kind of shamanish advice.

"He was playing everything from his Outside album and he said: 'You guys are going to destroy us on stage because we're not playing anything anybody wants to hear. Nobody really wants to hear this new album. What they want to hear is The Jean Genie and all the hits but I don't have it in me to do that now.' I thought that's kind of dumb on one hand, then I thought, to build something, a persona or a sound, and it's not broken and worn out, and then throw it out and try something new … man, it takes balls to do that. Would I ever have the courage to do that, or would I do careers and expectations and fitting in?"

Reznor's mellowing extends to his visuals. The video for the album's first single, Came Back Haunted, directed by David Lynch, is a miasma of indistinct menace and sea-monster deformity, but practically Rastamouse in comparison with some of the early promos. "There was a phase where it was 'let's see how far we can take it'. We did a compilation of videos for the Broken EP, the second record we put out, and me and [video director] Peter Christopherson were talking about snuff films. He said: 'Why don't we tie these videos together with this narrative as if it was a real snuff film?' I didn't hear anything for a while and then an unmarked paper bag with a VHS video tape arrives in the mail … I love extremity, and I thought let's not make it look fake, but we both agreed not to put it out. I mean I'm living in the fuckin' Sharon Tate house, it's enough."

What was in it? "Y'know some penis dismemberment, the basic stuff."

If Reznor's interest in being rock's premier provocateur has waned, his hunger for new challenges and innovations certainly hasn't. He's become a virulent critic of major labels, ditching Interscope in 2007 to experiment with online DIY distribution, releasing free streaming and download packages of his two 2008 albums The Slip and Ghosts I-V. He talks at great length about a new streaming service called Daisy he's working on with Dr Dre's Beats and Interscope Geffen A&M chairman Jimmy Iovine, envisioning a more musician-friendly rival to Spotify ("There's a puzzle to solve in terms of what would be something that from a consumer's point of view brings joy and from a musician's point of view could put some cards back on the side of the table of the music content creator."). Yet Reznor has announced a truce with the industry of late by signing both How to Destroy Angels and NIN to Columbia. Why? "I found that when I was putting my own music out, with my Twitter feed as the pure marketing budget, I'm preaching to the choir," he says. "I'm trying to figure out how to keep my head above water."

Fitter. Happier. Unstoppably productive. From self-loathing addict to artist and innovator; rock's moodiest outsider has finally clawed his way to the top of the spiral.

Nine Inch Nails play exclusive festival sets on the main stage at Leeds festival on Friday 23 August and Reading festival on Sunday 25 August.