A couple of years ago, you knew exactly where you stood with Scottish indie-folk bands.

Now they're spreading out in all directions at once – a shade more Americana here, a move closer to traditional folk music there, a mariachi trumpet blast, a grunge guitar crunch, an electro keyboard pulse – so that it's becoming increasingly difficult to pigeonhole the genre.

Take Glasgow's Three Blind Wolves, for example. I've heard Pavement and Frightened Rabbit mentioned in the same breath when they're being described. Inevitably Neil Young will come up as an influence, but once, when they were playing in America, someone in the audience reckoned they reminded him of Californian punk band Social Distortion.

I can hear all of that (well, maybe not the last one) in their debut full-length album Sing Hallelujah For The Old Machine. With its mandolin hues and narrative sentiments, I Will Put You In The Ground is country through and through, and Honey Fire aims for Fleet Foxes with its floating vocal harmonies; but the opening pair of songs – In Here Somewhere and Tall Man Riding – swing like The Band did back in the day. Personally, I'd pay this album one of my highest compliments: it would sit well on a late-night bourbon-sipping playlist alongside everything by Lucinda Williams and what Bruce Springsteen did in the 1970s.

One thing is for sure: Sing Hallelujah is a giant leap forward from the quartet's 2011 mini-album Sound Of The Storm. In broad strokes, the Americana has taken a small step backwards while the American rock element has become more prominent. That's probably down to the fact that Three Blind Wolves are such a formidable force as a live band. While the superhuman energy of their sets could previously get a bit out of control, they're now tighter as a group and this new album channels that vitality from the stage to the studio.

"You want to see a progression in a band," admits singer-guitarist-songwriter Ross Clark. "You don't want to hit out with the same sound all time. We're hungry for all of it, but this record has definitely taught us the patience of waiting. I've nearly lost my mind because I've got no patience for anything – I'm writing songs all the time. But we need to do this properly. That's why there are other people in the band, who can tell me to shut up."

Meeting Clark face to face in a Glasgow cafe, it's easy to see what fuels the Three Blind Wolves engine. Words pour out of him as his excitement about the imminent release of the album – preceded by a European tour supporting Canadian indie-rock band Wintersleep – rises to the surface. There's a confidence but also an honesty to what he's saying.

"I started playing guitar when I was at school, about 13, and I always thought I was born to write songs. You could say someone is a trumpet player or someone is a violin player; I'd say I'm a songwriter. I started playing gigs as soon I was allowed to get into pubs.

"I started playing in The Vale next to Queen Street Station – a baptism of fire. And I'd always play with metal bands because when I was about 17, there wasn't really a big acoustic session scene in Glasgow. There would be those albums you'd get in petrol stations with Badly Drawn Boy and all that, but 'acoustic' meant 'sappy' and the indie-folk thing hadn't started yet."

With guitarist David Cleary, bass player Kevin Mackay and drummer Fhearghas Lyon, Clark secured some early gigs in Japanese noodle bar Miso on West Regent Street.

"When I was playing, I'd just go mental, that was my thing," he continues. "I'd jump on chairs and be really loud and in your face because I was a big Billy Bragg fan who loved punk. But at the same time, it was when I was getting into Bright Eyes and Bob Dylan and getting washed over by all these different ways of being a singer-songwriter. I felt I needed to flesh out my songs more... I was writing songs, but the sound was the four guys. I wanted it to be a band."

Which band did he want it to be? While everyone else throws around valid reference points –My Morning Jacket, Modest Mouse, The Decemberists – Clark's contribution is unexpected.

"One of our favourite bands is The Funk Brothers, the Motown band. You listen to them and you hear them digging in, that's how good they were. If James Brown came back from the dead and said, 'Hey, guys, you can be my band' – OK, we definitely couldn't because he'd fire us in a second – that's what we aspire to: The Band during The Last Waltz, Led Zeppelin at the Royal Albert Hall, Crazy Horse doing Rust Never Sleeps."

Led Zep excepted, the influence from the other side of the Atlantic is pretty clear. So how did the crowd react when Three Blind Wolves took their US-inspired music to South By Southwest (SXSW) in Austin, Texas, last year as part of a Scottish showcase?

"Certainly, in the UK, people talk about our American influences," Clark admits. "But when we were in America, people just talked about our music. It's less about comparison to other bands and more about the way we are.

"After SXSW we went to Nashville for the first time, which was really intense because it's a big musicians' town. We walked into the venue and people turned around and looked at us. It didn't help that I was wearing a cowboy shirt and a cowboy hat ...

"But then we played our music and, after the gig, people were asking 'How would you describe your sound?'. So I said, 'It's country rock.' And they were like, 'Y'all ain't country rock ...'."