Earlier this year, his album DSU – rumoured to be an acronym for many things, including 'Dick Suck University' – sold out two limited pressings almost instantly. Since its international release proper last month, he's become the word on everyone's lips, not just those with a penchant for Bandcamp gems. It would appear that the record might be a bit special.

He's been releasing music via Bandcamp since 2010 – though making it for many more in the form of amateur techno as Rubberthump and The Skin Cells – releasing countless LPs, EPs and singles. He's been dubbed “the Internet's best kept secret” from a horde of outlets, but it appears that the world is about to break the first and second rules of Alex G club. DSU's release, on Lucky Number this side of the pond, makes it clear that Alex G, categorically not the YouTube star of the same name, is a phenom of the acoustic arts.

“I guess... I guess I'd have to describe it as just pop songwriting,” G says of his style. “Pop-rock? Yeah, pop-rock.” He seems unsure, blasé even. There's an impression he doesn't really want to label it as anything, and just let people figure it out for themselves; he's not a salesman, he's a musician.

Studying at Temple University, a grand ol' establishment in Philadelphia, G's grown a solid rep for his live performances as well as his recorded material. “Temple is pretty good 'cause there a lot of people who have shows in the area,” he says. “People would have them in their houses. Almost every day of the week there's these big parties with local bands or whatever, and even before I went there, when I was in grade school, we'd go up and play or watch someone play. I mean, part of the reason I went there is cause I knew it well from playing parties and shit!” It's not just about relishing the hedonistic options though. “It gave me an opportunity to play live a lot and understand the things people like, what kids are listening to and how to read a crowd. Music was a big part of the social scene in Temple. It's the reason why I was driven to do it in the way that I have done, 'cause it was so rewarding and people were so open minded about music and trying new things.”

Further back than the scenes of his formative college years, he's indebted to familial ties. It's that same way that so many are shaped by the music tastes of their immediate household – the way that you love Bowie 'cause your Dad does, or you'll always have a soft spot for The Cure thanks to your sister. “I would say, if it wasn't for my brother making music such a prominent part of the household, I don't think it would be like this right now. But it's like a butterfly effect. There's probably a million different things that happened that mean it wouldn't be the same. My sister played a massive part of the music I like to listen to. I idolised her.”

So, uh, thanks Giannascoli siblings. We owe you a beer or two.

“I know a lot of publications have called what I do 'bedroom' music...” G says, swiftly moving on. He's a shrewd mind when it comes to reading perceptions of himself. “I would never say that though, just 'cause I'm not trying to be this 'bedroom' guy, I'm trying to make it as high-quality as I can with what I've got. A lot people seem to like it for that reason though; like, it's not artificial. Unfiltered, maybe... I like to concentrate on the melody and the hook a lot. I do try and have an element that makes people uncomfortable as well though. I like to do that to have a depth, but I think pop does that too. That doesn't make my music not pop.”

Regardless of the label slapped onto his sounds, he does make most of his music in a bedroom, slaving away in isolation. “It was...not restrictive,” G begins, assuredly. “A lot of time I wasn't even at home, I was at my girlfriend's house, just messing around and stuff you know? I don't think it was restrictive except... except maybe for singing. I was pretty shy so I'd always wait until no one was around. Oh, maybe as well when I'd be playing a riff to record it without any flaws or whatever and that'd drive my room mates crazy, just hearing the same riff over and over and over...I'd have to stop and come back, as I was concerned about irritating them.”

Working alone has always been the modus operandi for G, holed up in a bedroom with decidedly un-pro equipment and no noiseproofing or big-budget sessioners. “My family got a Mac when I was in middle school, like aged 12/13 or something that came with Garageband, so ever since then I was fucking around with it. Before then I was playing keys and guitar, messing around but never really doing anything with music. I still use Garageband for my shit! Maybe I'll upgrade...” he says, before quickly changing his mind. “Actually, I dunno if I will. At some point maybe, since a wider audience will hear it so it'll probably be for the best. If I can still get the quality I want I'll go more pro.”

G's a prolific songwriter, with over 10 releases available – at the ripe old age of 21 – a feat most bands don't achieve in their entire lifespan. “When I was younger I made a lot more...” he humbly points out. “I was more productive, as I didn't have as much to do or as many responsibilities. It was always enjoyable – my go-to thing – because there wasn't much to do. I guess some kids like to draw, and I like learn chords.”

His modesty continues when acknowledging the links onlookers have drawn between himself and legendary singer-songwriter Elliott Smith. “I listened to [him] a lot when I was younger. Perhaps I was influenced by his structures, like just how complex he would make a chord progression; other artists do that too, but for some reason I got attached to him. That inspired me to put more effort into composing and shit. My chord progressions are subconsciously inspired by him, I guess, as it's probably ingrained in my head. There's tonnes of artists that have inspired me but he seems to stand out. Maybe its the singing style...I usually sing quietly so my room mates don't hear!”

But it's not just the overt inspirations that G wields in his music-making. There are subtler threads that burrow through. “I'm a huge fan of Aphex Twin. I really like electronic music. The Knife and Aphex Twin and Boards Of Canada are my favourites. I think that might surprise people. I go about making music the same way as a producer does; like them, I'm just one person trying to compose a whole track. I can record one layer and then sit with it fiddle with it, and it's not like I jam out to come up with stuff. Well I guess I do by myself, but my process and that of electronic musicians is similar.”

“Well I got it done a year ago.” G responds when asked if his process for DSU was like that of a producer. “I think it's a little less than a year ago, but then it got popular real quick. I wrote it over the course of two and half years. It's hard to say anything concrete cause the recording and writing process was so spaced out. Like, I'd think of a song at work or school and come back home and record, or sometimes I'd just be messing around on the guitar and record it. In between writing and recording DSU I finished other songs and put them online to keep people interested. I took a long time on the complete album as I was conscious of the audience at that point. I wanted to make it as perfect as possible and I wasn't happy with putting it out there unless I felt I'd got it down.”

And is it perfect, at least in his eyes?

“I don't think it's perfect. Nobody would say it was. I shaved it until there were no rough edges I could see. I think it has the minimal, essential components of each song and it doesn't need any more. I'm proud of what I've got.”

G muses on its construction and intentions. He says that it's not really like anything he's written and that he's looking to write something more “inspired” next time. “There's not any lyrical themes really. There's an overriding musical theme though. I like them to sound sweet, like you're listening to the radio. It's like radio pop but a little bit like you're in a dream as well. I wanted it to sound off-kilter. That's the theme: off-kilter.”

Despite saying that the lyrics don't follow any narrative arc, there are some links, at least from the outside. The subject matter is pretty much what you'd expect from a 21-year-old student: relationships (both romantic and platonic), a steaming dollop of adult anxiety, intoxication, inebriation, and cult movies (“Harvey” is based on the '50s flick of the same name that inspired Donnie Darko). Giannascoli is playing fast and loose with his emotions, delivering a cavalier attitude towards self-censorship, which results in a thoroughly honest LP. Peel back the layers of fuzz and you've got yourself a salt-of-the-earth anthology with an everyman streak.

Each track – despite sounding scuzzy and raw – boasts a hearty pop core. “Hollow” is soft, gently haunting and brittle, like a post-folk/Pavement ballad; “Promise” is a dream-funk with all the components of a great Metronomy-esque belter; “After Ur Gone” is scratchy, knee-graze fuzz-rock. It's this track that's been the figurehead for DSU's mission. G explains its simple origins. “That was actually written way before DSU or other albums. When I was a teen I'd smoke a lot of pot and just record. It was a really long song. I figured I could bring it to this album, so I just edited it down and made it fit in with the rest.”

It's hard to believe that even now that Alex G and DSU are fully revealed to the public consciousness, and he's ruthlessly plying his wares to the world, that his capacity for creativity is even slightly diminishing. “I'm always working on my shit,” he explains. “I think that DSU is a compilation of recordings from that time period of like a few years ago. Once I'm finished making music and I know there's a whole album's worth of material I edit them and make them more fluid and cohesive together. I have a couple more songs that I'm working at the moment on that I'll probably put out soon. I couldn't say for sure when they'd be done though!”

This year has been quite the whirlwind for Giannascoli. Less than 12 months ago you'd be hard pressed getting him to believe exactly where he's ended up, and all the successes that DSU has brought. “What's been the best thing to happen this year?! I don't know!” he says almost flustered, as if the antics of 2014 still haven't sunk in, which results in him praising the city planning department of the UK's capitol. “...coming to London has definitely been one of the best things. I love the way it's so curvy...Philadelphia is like a grid.”

Despite still reeling from the immense year, it's crucial to bear in mind how much of a beginning this all is for the 21-year-old. A beginning met with unanimous applause and promises of grand futures, sure, but a beginning nonetheless. Giannascoli's been peddling noise for years, and there's little that'll get in the way of him continuing that, come rain or shine, audience or no audience. The most vital part of the future for Giannascoli isn't riches, flashy cars or a fawning fandoms; dignity and creative integrity are his only aims. “I will just do anything that means that I can have total control over the music,” he says, before tacking on a caveat, almost for his own peace of mind. “I'd like to have another record out next year, but I don't know. That's my goal.”

DSU is out now on Lucky Number. Alex G returns to the UK next March.