It's 3 PM in Hamburg, and DJ Koze has just woken up. He doesn't fall asleep until 6 AM most nights, and it's been like that for a while. It might be from the travel. After all, Stefan Kozalla is one of dance music's busiest DJs. His schedule has taken him abroad for gigs most weekends for the past 15 years. Kozalla has emerged from a nearby apartment building overlooking Hansaplatz, a square in the centre of the city he's lived in for around two decades. "My rhythm is switched," he texted after I tried to bring our meeting time forward a few hours. "Feels better to talk not before 15. Sorry." But he's here now. Walking over in baggy pants with an outstretched hand, Kozalla has the vacant look of someone who's had a bad experience with an alarm clock.

For a Tuesday afternoon, the streets are bustling. This port city of just under two million is home to a small but strong electronic scene, some of which revolves around Golden Pudel, a small club with an exceptional music policy and world-class residents. (Kozalla once fell through its roof, only to land, as he proudly told me, standing upright, completely unscathed.) Then there's Smallville and Dial, two labels that helped shape the sound of deep house throughout the '00s. There's also Diynamic Music, a label and collective founded by Adriano Trolio and Solomun, the only Hamburg house DJ more famous than DJ Koze. It's hard to see where Kozalla fits in here. As time goes on, he sounds less like anyone else.

"See those women over there?" He nods towards a pair of middle-aged tourists in bright puffer jackets. "They've been following me for three days." He pauses. "Not really. That's just my paranoid brain." It's impossible to tell if he's serious. We find a seat at a cafe on the edge of the square, but once we sit down, it's clear that Kozalla is nervous. He can't sit still, constantly shifting in his seat and picking his fingernails. It's a different person from the one you see drinking champagne from the bottle while blending tracks in front of thousands, or posing in fancy dress on album covers, including Knock Knock, the one he's been working on for the past four years.

It's a few weeks before the release of Knock Knock, his third album as DJ Koze, so we've caught him at a particularly busy time. He's in the middle of a long string of interviews, which, for someone who seems to take a while to warm up to strangers, can't be easy. I can already sense that he'd rather be doing something else. "It's a nightmare," he says as he wriggles from side to side. "I don't like it. But I have to do everything possible to bring the music to the people."

That music is the mixture of house, hip-hop and folk Kozalla has been pushing for close to 20 years. Raised in Flensburg in Germany's north, he's been a full-time musician for most of his adult life, beginning with his role in Fischmob, a hip-hop group active throughout the '90s. He's only ever had one full-time job, working in the design department of an advertising agency before transferring to the copywriting team. Kozalla's sound is rich and emotional, heard in spellbinding tracks like "XTC" and his remix of Matthew Herbert's "It's Only," both of which float in the powerful zone where melancholy and euphoria intersect. Hazy and vague, the focal point in his music is rarely the rhythm, which in Kozalla's case moves between a soft four-on-the-floor pulse and stunted hip-hop patterns. Sometimes there's no beat at all.

"It's the most stupid signal," Kozalla says about the pounding kick drums he hears at almost every big event he visits. "I don't know how people are still fascinated by this thing."

This attitude puts Kozalla at odds with large chunks of the scene. At events all around the world, especially the huge raves and festivals Kozalla plays at, fat kick drums seem essential. Modern production techniques allow artists to make their tunes heavier than ever; so heavy they can overwhelm the older tracks they're mixed with. Tracks like Kozalla's, which bury blunt kicks deep in the mix, are rare. Instead of rhythm his tracks emphasise texture, dazzling with the vocals, melodies and bleeps he endlessly tweaks in his Hamburg studio. Every element, whether twisted from a sample or pulled from a synthesiser, is deeply considered. This results in sounds that feel abstract yet warm, evoking feelings that you can't quite describe.

These days, Kozalla isn't too concerned with making tracks for the club. He's made plenty of party-ready tunes, dating back to the early '00s, but the dance floor never seems to be a priority.

"A straight bass drum can be Luke Slater or it can be Gas," he says. "Jan Jelinek also has a straight bass drum, but it's not that important. The music is super emotional, but nobody would say that it's because of the bass drum."

Kozalla pulls his sunglasses from his shoulder bag and shows them to me. They're heavy and kept in a case, so I assume they're expensive. "Two euros from a Chinese store," he grins.

Our photographer, who's been taking photos from across the table the whole time, slips. Comfortable with his new position half-sitting, half-lying down, he begins shooting from knee height. Kozalla protests. "I have the feeling that from below I always look sick."

"But powerful?" the photographer asks.

"From above I look more powerful."

Underneath Kozalla's melancholy tracks and musings on music, there's a mischievous streak. It's there in the way he plays for the camera, throwing hip-hop signs and posing with his sunglasses. In front of the lens, he stops fidgeting and focuses his attention ahead, putting his sunglasses on, removing them and putting them back on again.

"There's an idea in the music that doesn't need to be the club," he says between poses. "We all come from the club, knowing how it is to be high. But this music can also work at home. If you do a loud kick drum, you don't want to listen there. You go to the stereo and think, OK, here's a nice track, but I'm in the kitchen and why should the bass drum hammer through the flat?"

Perhaps more than anything else, a sense of emotion is central to Kozalla's music. His tracks have moods that might change depending on yours. Take "XTC," a slow-burning deep house tune with bright synths. Everything about the mellow beat says summer dance floors, but uncertainty runs through the vocal, inviting more questions than it answers. The same goes for "Pick Up," a track from his new album. The looped disco break and strings ooze good vibes, yet the sampled lyrics, taken from "Neither One Of Us" by Gladys Knight, are pure heartbreak. Kozalla's tracks are conflicted, which might be the best way to explain the producer himself, who's like a class clown who writes poetry at night.

"I have a good life," he says. "But I'm too fragile and sensitive. I'm always judging myself. The older you get, the higher your standards. You can listen to the nicest music in the world, so why should I do something that is not that good?"

Kozalla spends weeks at a time tweaking melodies and samples, running them through plug-ins and effects pedals until he gets the sound right. This craftsmanlike approach shines through his music, which feels effortless and awesomely detailed at once. Listen to how the percussion pans around the stereo spectrum in "Pick Up," or the way the synth melts into the sampled piano chords in "Seeing Aliens," two tracks that capture the duality of Kozalla's music. Reaching from the sun-kissed haze of "XTC" to the stoned hip-hop of "Baby (How Much I LFO You)," a highlight from Knock Knock, his sound constantly shifts. There may not be a more multidimensional house producer on the planet.

"I don't want to talk about negative things," Kozalla says. "But the mood of house music is really limited. It was sensational for me to discover Kerri Chandler, for example. I thought, wow, this is deep and cool. But I began to hear more emotions in folk music. Why do we have to stick to two house chords? This is what I'm trying to work on. We can have more emotions in this music, but we have many formulas that always sound the same. And the blessing and the curse is having software synths—everybody can immediately make music that sounds like everybody else. This is a problem."

Kozalla's DJ sets also aim to reach a range of emotional states. He's the kind of selector who can mix big-room tech house with disco, or who plays a string of house tracks with the bass cut off. Where most DJs of Kozalla's stature take a direct, linear approach, he brings the energy up and down often, cutting the bass from both channels and playing with the faders while blending tracks. He's a master of tension and release. It's not about instant gratification—he rewards dancers with the patience to stay locked in for hours.

"The most fulfilling thing is not to bang the shit out of the club," he says. "People are longing to be relieved. If you relieve from the first minute, they can say, 'Wow, this is a sporty, hard guy. He kicks me hard in my ass. Respect to this dude. He has the bass drums.' But I'm not that guy."

His approach can be entrancing. Crowds scream for Kozalla to play his best-known tracks, like his remix of Herbert's "It's Only," and dance to them with their eyes closed and smiles on their faces. "This is a fascinating thing," he says. "I was playing in Aberdeen last week to a young, hard and drunk crowd. They needed hard and banging music, but I played this Herbert track everybody became soft like a sheep. I thought, wow, these hard guys, you can make peace with them through music." I saw him send Panorama Bar into meltdown with Felix Da Housecat's "Kickdrum," an intergalactic drum track most house DJs wouldn't touch.

But Kozalla's style doesn't always land. He jokes that he wasn't invited back to Amsterdam's DGTL Festival because of his 2017 performance there. By not following the straight-ahead path of conventional house and techno sets, Kozalla takes a risk each time he DJs.

"I fail if I don't catch the vibe," he says. "But I need to be brave and combine new ideas to keep it interesting. You can't lose your focus and find a formula. You see it at the end of the season, when DJs don't care where they are because it's their 80th gig. And they play a big-room set in a small club, so you see he's just on autopilot. If I was only on this mission—a functional mission—I would get depressed."

I believe him. Kozalla feels intensely genuine, and not the kind of person who has something to prove. But there's doubt underneath it all, manifested in the way he sculpts new tracks, only to delete them when he doesn't get the results he wants. "I work on many tracks," he says. "In the first moment, you're rushed that something is finished. But after a week, you compare to this track that moves me and that track that moves me, and you realise it's not that good. You think, shit, I can't believe what I'm doing with my time."

DJ sets also bring stress, to the point where Kozalla is unable to shrug off bad nights. "Sometimes I'm scared to look in the first row," he says.

Why do any of this then?

"Because I want love," he says. "This is the only answer. You want to be part of this output, to make changes and leave your fingerprints. You want to add something to the discourse. And you want love and feedback. This is a beautiful feeling—if you don't make compromises. Otherwise you get feedback for something that isn't you."

For Kozalla, finding new music to play is tough. Yet alongside the hundreds of big-room house and techno promos he's sent each week, there are still records that get him excited, and most of them aren't conventional house and techno. "I like it when they don't use the spectrum of what's possible," he says. "If it's too dirty, it's a statement. And if they don't use cheesy plastic sounds. It's good if I hear an organic groove, and a dirty or warm sound, and no elements wanting some specific reaction."

He particularly likes Shakarchi & Stranéus, a Swedish duo signed to Studio Barnhus, one of the labels that lands closest to Kozalla's sound. The duo's first album, Steal Chickens From Men And The Future From God, just dropped, and Kozalla loves it. It sits somewhere between the home and the club, a mix of flamboyant disco and house with a few bangers and a few more abstract tunes. "They don't kill it by fulfilling it," he says. "There are hi-hats, shakers, strings. Everyone is waiting for the kick drum that doesn't come. They stay and keep the tension. Other producers would say, 'This is a nice melody, you can put a fat bass drum and make a hit for Ibiza.' But they were brave. If you don't fulfil, it's nice."

Noticing the silence, Kozalla's sarcasm surfaces. "And now the wise man is speaking," he says with a smirk, relaxed enough to crack a joke.

We decide move to another spot, aiming to take a few photos along the way. Back in front of the camera, Kozalla gets new energy. He's brought a few scarves to pose with ("I'm a professional," he says) and starts throwing hip-hop signs and trying to make us laugh.

We reach the park. The average age seems to be about eight years old, but that doesn't stop Kozalla from commandeering a swing from a little girl. After a few rides, we make small talk about Hamburg and visit what could be the nicest supermarket in the city. Kozalla buys us cucumber-flavoured soft drinks, a personal favourite of his, and is disappointed when it seems like we don't like them as much as he does. (For the record, they were great.)

It's about 6 PM, which means that, by Kozalla's clock, it's almost midday. He'll be meeting his girlfriend soon, so it's time for me to head back to Berlin. "I think you have enough, no?" he asks, but it's not really a question. More energetic than ever, he has the mood of someone whose day is about to start, not end.

But what does he do during those nights he can't sleep?

"I think about my ruined life."