A couple of years ago, Courtney Barnett fell in love. She was living in Northcote in Melbourne, just around the corner from Thornbury Records. A Sea Of Split Peas, her breakout double EP, was still a way off from being released, and she was trying hard to make it as a musician. She’d spend her days writing songs, her evenings playing gigs, and any spare time she had at Thornbury, where she’d bug the attendants for album recommendations.

One day, the person behind the counter suggested Kurt Vile’s Smoke Ring For My Halo. She hadn’t heard of it, or of Vile. “I’m not very clued into stuff,” Barnett says now, over the phone from Europe, where she is touring with her wife Jen Cloher. Her voice is rich, and she’s quick to laugh, which she does now. “That’s why I need recommendations.”

I love music and I love watching shows, but when you really connect with something… It’s rare.

She took the album home, chucked in on, and then it just happened: she was smitten. “I loved it,” she says. “And I still love it. I think it’s one of the most beautiful sounding records that I have ever heard. And the songwriting is amazing. It was just this real discovery – it was something that I really, genuinely loved.

“That doesn’t happen that often for me with music. I love music and I love watching shows, but when you really connect with something… It’s rare. And where I was at at that point in my life – that meant the record went through an extra layer of importance.”

Barnett can still listen to the record now and feel the same way. It is one of those oddly nostalgic albums for her – kind of like one of Proust’s madeleines; a trigger. She can put it on and be transported, wholly, back to that time in her life; can use it when her own memory fails her. “It is such a strong connection that I have to that record,” Barnett says. “I love it so much.”

The pair wouldn’t actually meet in the flesh for a number of years – not until A Sea Of Split Peas was out, and Vile came Down Under to promote his record Wakin On A Pretty Daze. Barnett managed to get added to a show he played at The Abbotsford Convent at the last minute, and they bumped into each other there. “That was a big deal for me,” she says.

“It was really cool. That was the first time I met him, but I don’t really remember it – we were packing up to go home, and they were going out on tour. I think I gave him my CD that night.” She laughs. “It was such a nerdy thing to do. But I’m glad I did, because I think that’s the first time he had listened to my music.”

For his part, Vile says he knew of Barnett before she gave him the CD. “I had heard of her,” he says. “But I didn’t really know her stuff.” He listened to the CD when he got home, and quickly began to feel the same way about Barnett’s music as she did about his. “Her lyrics were so totally great and real, and her voice was really pretty too. Her guitar playing was so great. She was a really great multi-instrumentalist too.” He laughs. “She just had this kind of glow about her, you know?”

October will see the release of the new album Barnett and Vile have made together. It’s called Lotta Sea Lice, and it sounds exactly as you’d imagine a collaboration between the pair to sound: effortless, full of warmth, big-hearted. Lead single ‘Over Everything’ has the two of them passing vocal duties back and forth like a baton, and their ease and grace with each other is so palpable you’d think they had been doing this for years.

But the record came at a strange time for both of them. Vile’s career had unexpectedly transformed after the release of B’lieve I’m Goin Down…, and that album’s exceedingly popular single, ‘Pretty Pimpin’. B’lieve got a lot of critical praise, landing on a bevy of best albums of the year list – but a lot of Vile’s other records had been similarly adored, and it was more Vile’s newfound commercial heft that so quickly changed things. Suddenly he was, if not a household name, then a viable economic prospect; a radio-friendly unit shifter in his own right.

It was weird, and Vile didn’t much care for it. “All the growing pains were so stressful at first – just like, trying to get professional,” he says. “It was crazy. Like, the last couple of tours we did for that record, I was so tired and burnt out, and I didn’t want to go, but I did. Luckily, they ended up being the best shows that we ever did.”

Post B’lieve, Vile found he couldn’t fall back on old routines anymore: couldn’t stand there onstage with his long hair covering his face, and play a whole set without ever looking at his audience. “I used to be more like that; paranoid,” he says. “I wouldn’t even look at the crowd too much. But I think the crowd could sense I was nervous and weird about it. So slowly I started looking up more.”

On the other side of the world, Barnett was similarly feeling scraped thin, and was becoming just as confused as to how she might best proceed. Sometimes I Sit And Think, And Sometimes I Just Sit, her debut album, had changed things forever. Between its best new music rating on Pitchfork, and Barnett’s televised appearances on everything from Ellen to Saturday Night Live, she had become a genuine cultural force.

I think not being at the kind of front and centre of the stage definitely is a lot less stressful.

Americans were lapping up her songs about Vegemite, and deceased estates, and the slow death of the great barrier reef, and even by early 2016, the cries for a follow-up record were growing. It’s like they say – you have your whole life to write your first album, and a year to write your second.

But Barnett didn’t want to rush anything. She decamped to the coast to play on Cloher’s excellent self-titled record, and she tried, as best as she was able, to lay low for a little bit. When the opportunity to tour with Cloher came up, she jumped on it. “I love playing with her,” Barnett says. “I think not being at the kind of front and centre of the stage definitely is a lot less stressful. It’s fun. I don’t know – I just love being the supportive guitar person when playing [Cloher’s] songs, because I love her songs. I just love standing and watching her play. It’s great.”

Simultaneously, Barnett’s friendship with Vile blossomed. “Over time we discovered we had mutual friends, and we kept running into each other in festivals,” Barnett says. “We just became really good friends.”

But Barnett had no concrete plans for the pair to collaborate. It wasn’t a creative relationship; it was a, y’know, normal, regular one, and it wasn’t until she woke up one day to an email from Vile that she even entertained the option of the pair writing together.

“Kurt just emailed and was like, ‘I’ve got this song I think would maybe work for both of us to sing,’” Barnett explains. “And then he was coming to Australia to do some touring, so we found a day off and booked a studio. It all just fell together.”

Even then, the pair thought the collaboration would amount to, at best, one song, or maybe even just a tour. They did not want to ask anything of their nascent friendship – didn’t want to put any kind of weird pressures on it. And anyway, they’re not really the kind of people to trap themselves in tight spots if they don’t have to.

“The tour was kind of booked before anything else was even really thought of,” Vile says. “It was just the electricity of the moment – everything just kind of came together from that first point of contact. We never were like, ‘We have to get this many songs’ or anything like that. It just sort of happened.”

“We never planned to write a whole album together,” Barnett agrees. “A second song just came along, and then we did a cover, and we were just having fun in the studio. And then we kinda just hung out and mucked around, and then we went off on tour again, both of us separately, and we had these three songs. We did pretty much a year of touring, and we kept seeing each other; bumping into each other all over the place.

“But we still had no plans for an album. We just had these random songs that we made. And we kept talking about it; we were like, ‘Shall we do more songs?’ So we booked some more studio time. I had another song, and he had another song, and it just kept on happening.”

Barnett laughs. “Then when we had ten songs, Kurt was like, ‘Well, that’s an album. Let’s just put it out.’”

Because nobody knew Vile and Barnett were writing an album until they had actually written an album, there was no-one breathing down the pair’s necks. They had to face none of the pressure that they would have if they were recording their own follow-ups to B’lieve and Sit And Think respectively; none of that paralysing sense of expectation hanging over them. It was like they were working under names other than their own – like they had faked their own deaths and started afresh.

“I think if we went in there to make an album, our mindset would have been different,” Barnett explains. “The mindset of everyone around us would have been different too – like our managers, and even the producer of the record. Because if it’s an album, everyone is like, ‘Ooh, this is a big deal, you know. We better do this really well because it’s an album.’

“That kinda freaks me out. ’Cause everyone reacts to that kind of pressure differently – and it would have been this weird pressure on me. What we managed to do instead was just capture this really beautiful, totally spontaneous thing.”

I think whoever you play with, something always rubs off on you, you know?

It would be unfair to suggest Lotta Sea Lice had no purpose but to provide a little bit of creative breathing room for both of its artists, or to imply that it’s anything but a fully fledged, exceptional record in its own right. But at the same time, it did have a recuperative effect on Vile and Barnett. It reset them. They went into the studio a certain type of musician, and they came out changed.

“Every process is different, which is kind of the fun of doing all these different musical projects,” Barnett says. “You learn something from each different performer. It’s not all the same kind of boring repetition. I think whoever you play with, something always rubs off on you, you know? I just think being around different people and having different experiences in general, it’s always going to kind of paint who you are a little bit each time.”

Vile agrees. “I just stumbled upon something really cool with Courtney,” he says. “She’s just really enthusiastic. She loves music. Everyone I play with loves music, of course, but some are more cynical – and she’s not at all, so it’s really fun playing with her.

“I think two equal people bringing different material to the table and helping each other where needed or just being inspired to work together – that makes you want to step it up. That kind of energy; you can’t predict it. You can’t force it. Something just happened.”

Later this year, the pair will go on tour together, taking their newly formed supergroup The Sea Lice around the States with them. Cloher will open a number of the dates. Neither Barnett nor Vile really know what that experience will be like yet – Barnett has the suspicion it might be a little like a “variety show”, and Vile is looking for the opportunity to “share the spotlight with Courtney.”

But no matter what happens, they will always have Sea Lice, that beautiful accident of an album. “I listen to the songs now, and I just feel happy,” Barnett says.

Lotta Sea Lice is out through Remote Control on Friday October 13.

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