"Every Thursday is Glamma Rays day," band member Tiffany Sinton says. "We just know that we rehearse then, or have meetings or photo shoots or whatever we have to do. We just plan it for a Thursday and it all fits."

The band sings four-part harmonies in the style of the Andrews Sisters or The Supremes. But unlike other a cappella groups, the Glamma Rays only perform original tunes.

"It comes easy," Sinton says of songwriting.

"My parents were in the jazz scene and I was brought up on jazz, listening to 78 records and that sort of thing. Jodi [Phillis] had the same background and the other two girls have a real sensibility for jazz.

"Our writing comes very naturally but Jodi Phillis is a musical genius in terms of arrangements. We all take turns at writing songs but she'll do the harmony arrangement for them. She's amazing at getting that old-school girl-group sound."

The group has been together for four years and, aside from some musical accompaniment on guitar from Phillis or ukulele from Malika Elizabeth, it's just the four voices on stage (the fourth member is Genevieve Davis).

Sinton says performing on stage without a band can be tricky - but the audience does respond well to it.

"Vocally it means you're really vulnerable, it's really just you and your voices there on the stage without lots of noise and drums and everything to hide behind," she says.

"It does put you in this really vulnerable place but I think it's also really honest. I think that's something that really pulls at people's heartstrings because it's just so real and honest and just beautiful. Also, we create such a full sound anyway because we've got four different voices happening, we're never all doing the same thing. It's not like when people write harmonies nowadays where they'll follow the melody - we're going all over the place."

This Friday, the band is launching their first album, Listen to the Birds. Largely recorded at Phillis' studio, along with a few tracks from live shows, it's a release that's been more than a year in the making.

The tracks in Phillis' studio were recorded in 2013 and the ultimate release took a long while because the band wanted to ensure they had the right feel.

"When we we're on stage and it's just the four of us singing at the same time, you capture the vibe and even the vibrations between the voices," Sinton says. "You can't capture that so well when you're laying down one track at a time.

"So we try, sometimes successfully, sometimes unsuccessfully, to record all standing around one mike.

"It's so hard to get everything perfect; one person just has to be slightly flat or make a mistake or hit the microphone stand and you're recording the whole song all over again. So it's just taken us so long and so many takes to get a take that Jodi's happy with. So it has been a long process."

The Glamma Rays, Listen to the Birds CD launch, April 24, Anita's Theatre