The Irish singer-songwriter's soulful, husky voice has drawn comparisons to everyone from Janis Joplin to Florence Welch. U2 megstar Bono is among her fans.

Yet O'Neill, known on stage as SON, admits it took a little time to find her voice.

"When I started singing, my voice was very high and I was probably very squeaky," O'Neill, 29, laughs. "I was finding my feet.

"I think everyone can sing. The thing is, I just kept doing it. I just wouldn't stop, so it got to a point where people had no choice but to listen.

"Years ago people probably questioned the ability [laughs], but the voice is like a muscle, you know, and I think the more and more we use it, the stronger that it can get."

Since releasing her debut album Found Myself Lost in 2017, O'Neill has become a crowd favourite at folk festivals.

Her live performances have won praise, not only for her ability to showcase her incredible range as a singer, but for her talent as a multi-instrumentalist whose sound effortlessly shifts between folk, blues and pop.

She returned to Australia last week for a two-month tour taking in almost 30 dates, including sets at Port Fairy Folk Festival, Blue Mountains Music Festival, Canberra's National Folk Festival and Newcastle Spiegeltent before wrapping up her tour in the Hunter Valley at The Gum Ball on April 24 to 26.

"What I noticed last time I was there is there's such a beautiful scene and a beautiful respect for the players," O'Neill says.

"People are very much ready to be taken on a musical journey. From that first tour, which was six weeks, the second tour was seven weeks and this time I'll be there for two months, so it's steadily getting bigger and longer."

O'Neill allowed herself eight weeks to record, mix, master and package her latest album, Inside Outside, which has been released as a special edition for the Australian tour.

The album embraces sounds from African, Arabic and Irish traditions, as well as her gospel roots after O'Neill reunited with members of the Ennis Gospel Choir in her hometown of Clare to record vocals.

It was a defining moment for O'Neill, who recalls convincing the director to allow her to join the choir as a determined 15-year-old.

"I begged to be in that choir, like, 'Please let me in, you don't know how much this means to me'," O'Neill says.

"The choir director was hesitant saying, 'I don't know ...', because you had to be over 18, but I said, 'Let me audition'.

"I can't even remember what I sang for her - it was probably something from Sister Act [laughs]. I went totally gospel. She said, 'OK. You're clearly in love with music'."

The choir features on two songs, including the title track.

"When I came home and discovered the choir is still going, I thought 'What a beautiful way to reconnect with everybody'," she says.

"I went in one day and taught them the chorus in one of the songs. The first song was so enjoyable that I came back the second night and said, 'Can I take some more?'.

"So they actually feature on two songs, which is really lovely."

O'Neill's dedication to music was apparent early on. At 12, she joined the local brass band and learned to play cornet and trumpet.

She has since added guitar, harmonica, whistle and congas to her repertoire, and uses a loop pedal on stage to create her distinct sound.

"I was always singing at home or tapping my foot, so for as long as I can remember I was singing into fake microphones or hair brushes. I loved it," O'Neill says.

"It was my strongest subject in secondary school. It was my favourite thing in primary school, then I went to college and studied music.

"When I finished I started to play around and then eventually you look for a bigger expression. I started to write my own songs. I learnt in the most organic way.

"I didn't approach it like a business, you know, 'Where do I see myself in two years time?' Music has always been there and I guess now I'm still doing it, but in a different way. Every day I'll take it down a new path."