"The first time I saw my voice coming out of Liam's mouth felt very strange."
James Walsh, lead vocalist and songwriter for Starsailor, is reflecting on the unusual experience of putting his distinctive sound in someone else's mouth, in his case actor Liam Boyle, for the character of Keva, in the film Powder.
While music is normally laid down after the film is made, because Walsh's soundtrack was so integral to the narrative, he had to work in reverse, providing a characterful musical bed without any footage, instead working from inside his head.
So, for a charismatic frontman used to showing off his talents on stage, did it challenge his ego to have to hand this over the finished goods for someone else to flaunt?
"Not really," he explains cheerfully. "I acted in college production when I was 16, and I was absolutely dreadful, so I was quite happy to leave the acting to the others."
Letting go was equally part of the deal for fellow Lancastrian, Liam Boyle, the young actor who plays Keva, who was already making huge preparations to sing the role as well as act it, until the production team got hold of Walsh's more established vocal talents:
"It wasn't certain whether James was going to sign up for the voice, so I had loads of singing lessons," he remembers. "I was practising with the band behind me, and there's a massive difference from singing in the bath, it makes you appreciate what musicians do...
"I was so pleased to be able to work alongside James. If I'd had to do it, it would have been a lot more work, plus James' voice was able to tell the story of Kiva in a way I'd have never been able to do, so I was really relieved and pleased. I think James' voice sets it apart.
"But I had to really study him and the way he sang, so it didn't look like one of those dodgy films where the miming ruins it. I wanted it to work, so the viewer is really transported and can forget it's not me.
"I'm a really big critic of myself, and the way they've cut it, you can't tell, it genuinely works with the sync. It's the first music film I've seen where the miming works."
The last time I saw James Walsh in action, he was trying, and failing, to make some grand rock star gesture with a twirly microphone, which ended up curling around him, Jungle-Book style, and toppling him over on stage at the Isle of Wight festival. When he is reminded of this, he has a very good-natured laugh at the memory:
"You can't be introverted," he reflects. "You've got to try and put on a bit of a show, be prepared to dangle the mike and fall flat on your face. I probably just thought, 'hmm, won't try that again.'"
Powder, based on the novel by Kevin Sampson, charts the rollercoaster existence of someone trying to make it in the music business. This is something Walsh must know a fair bit about, based on his decade with Starsailor, which has included chart success (with the critically-acclaimed album Love is Here), solo efforts, a feud with both of the Gallagher brothers, and - bizarrely - the unusual experience of having to sack Phil Spector from producing a Starsailor album.
"I was definitely at a crossroads," agrees Walsh, who was already friends "through football" with Powder director Mark Elliott.
"I've done a soundtrack for another film, and I have three songs on the new Matt Cardle album. I was wondering if I could do something new and that email came from Mark and started me on this other road."
Walsh jokes that he brought "wisdom" to the project, working with much younger musicians The Rascals for this film, his first, while they brought "the energy, definitely".
And the perils and privileges of rock star life - was this something he was able to provide an expert insight into? It seems not - unexpectedly it seems being a frontman with all the attention is not always all it's cracked up to be:
"The rest of the band did it on my behalf.
"I remember we went to Australia, and I spent the whole time in a hotel room with the guitarist doing a ton of interviews, never went outside, came home again.
"Then the drummer and keyboard player came back, with holiday snaps of them smiling and waving in Sydney Harbour, so they had a completely different experience."
Powder is available now on DVD. Watch both James Walsh and Liam Boyle in musical action below: