"The main thing is to have it be structurally exciting," says singer-guitarist Geordie Greep of the band, which will tour the U.S. in the fall.

Boosted by word-of-mouth and YouTube comments that have put them on par with art- and post-rock bands ranging from King Crimson to Shellac, Black Midi -- the London-based rock quartet that started attracting an audience after playing shows at Windmill Brixton, a divey hangout for indie-spirited DIY musicians -- is already on tour before its debut album, Schlagenheim, arrives June 21 on Rough Trade. Although they aren’t yet old enough to legally buy a drink, vocalist-guitarist Geordie Greep, lead guitarist Matt Kelvin, bassist Cameron Picton and drummer Morgan Simpson are bringing their vigorous experimental rock to Europe and then hitting U.S. shores in November (full dates here).

In an age of music that’s all about teasing and leaking, the band didn’t do much to fan the flames of its nascent success. “We didn’t think it was necessary to be posting as much as people do. That’s not to say there’s anything wrong with that -- it’s just we didn’t think it added anything to the music,” says Greep, 19, who was “home, chillin’” in London the day before the tour, which launched June 10, whisked Black Midi away from home. “Also, when we first got going playing gigs, it picked up quite quickly, so we didn’t have the means or the time. We thought we’d only record something when we had absolute control and be ambitious with it. We didn’t record our sets for a long time just because we wanted to wait until we could do it properly.”

Instead, the group continued playing shows, delivering dissonance, delicious syncopation and lyrics both muttered and shouted. Schlagenheim shows a band that plays together (no click tracks here) and stays together through abrupt tempo shifts, supreme agitation and movements ordinarily ascribed to classical music and prog rock -- but in a fraction of the time span. It sounds free and unaffected, conjuring post-punk, jazz and even overtures for a stage production or the big screen. Like the band Can, Black Midi sounds unencumbered but sophisticated, led by instinct, atmosphere and rhythm.

Upon graduating from performing arts academy The BRIT School in 2017, Black Midi found a fan in Tim Perry, who books and promotes shows at the Windmill. “Most venues are just interested in putting on bands they know people will come and see -- which is fair enough, they’re a business,” says Greep. “The great thing about the Windmill is that Tim Perry has eclectic musical taste. He made his name there by doing nights of country and hip-hop. He’ll put on anything that he thinks is pretty interesting. I sent an email to him. We got our first gig at the Windmill almost a month after we finished school, so it was quite lucky, really. I didn’t have a plan or anything for after [graduating] school. I definitely didn’t think this would pan out the way it has. So to play the Windmill and for it to go as well as it did is amazing.”

It was at the Windmill, where Black Midi eventually established a residency, that it met producer Dan Carey, whose own singles label, Speedy Wunderground, emphasizes spontaneity -- an ideal match for a band that thrives on improvisation. Upon hearing Black Midi, “Dan Carey got it straight away. We met up at his house and talked through it just to see if it was the right thing to do,” recalls Greep. “And when we recorded that track [“bmbmbm,” the first song the band ever recorded] for his label, it went really well and started such a good relationship, so when it came time and we had the means to make an album, he just seemed like the best choice. I could just tell from the way he was talking about the music that he got it completely.”

There’s a lot to get. Schlagenheim was recorded in five days, but its nine tracks sound anything but hasty. They do, however, feel urgent, with noisy, discordant patterns giving way to quiet areas of melodious guitar strumming and ominous verses, then re-sounding the alarm at twice the speed, then slow-motion collapsing in a pile only to rise again… and that’s just the opener. An entire album of such bracing rock would likely satisfy Slint lovers, but Black Midi is not interested in being the second coming of any band, so Schlagenheim proceeds to skitter, beep, groove and shriek. By album’s end, it’s impossible to decide on a genre or a particular audience for it.

Likewise, the band admires composers and musicians who relish changes in time signature and key. “We will listen to loads of different types of music,” says Greep. “I’m big into classical and avant-garde: Stravinsky and Bartok, and Alfred Schnittke, a really fantastic composer of the last 100 years.”

For the group's own music, “we do quite a lot of improvisation, get the best fit and put different things together, like two separate pieces of music,” he says. “We’ll have things lying around for a long time and then finally find the right section to complement it. The main thing is to have it be structurally exciting. Like in classical music: to have the music be really tense, to have that constant tension and release. We’re trying to push ourselves more and more compositionally, musically, every way we can.”

That improvisatory spirit is what makes the album such a thrill. It takes deep curiosity and un-self-consciousness to produce a work that is hardly guaranteed to be everyone’s cup of tea — and musicianship to pull it off.

“Make of it what you will, listen hard, keep listening,” offers Greep, a refreshing message that Schlagenheim transmits.