Irish musicians learn traditional jigs and reels by playing them in sessions. These jamlike gatherings, at parties and in pubs, have their own particular etiquette. For instance, apprentice bodhrán drummers generally aren't welcome because loud rhythmic lapses screw things up for everyone else. (The legendary piper Séamus Ennis once quipped that the best way to play the frame drum was "with a knife".) Another unspoken rule is that you don't introduce original tunes into the session, as no one will be able to play along.

So for years Liz Carroll's prodigious talent as a writer of traditional tunes went largely unknown. The Chicago-born fiddler, who currently plays in a duo with guitarist John Doyle, has forged compositions in the Irish mould since her childhood, but only her family got to hear them. She certainly didn't play any when, in 1974 and '75, she won the coveted All-Ireland Championships' junior and senior levels–becoming only the second Irish-American fiddler to do so.

"I've always written because I love to, and, because there never seemed to be enough tunes around, I wanted to create little challenges for my fingers and my ears," says Carroll, on the line from her Windy City home. "That's the reason I learned every damn tune I could hear. You didn't want to be left out."

These days, Carroll is happy to be making albums and getting her original compositions in circulation. Tracks like the achingly soulful slip jig "For the Love of Music" and the wild-swinging reel "The Potato on the Door", both from 2002's Lake Effect, are destined to become favourites at Irish-music sessions from Sydney to Sligo.

"When I was really young, my tunes didn't sound like anything that would get played," she remembers. "Then they got nicer, and then they got complicated because it was all about getting around the instrument–more about difficulty than melody. Later on they're all about melody, and they don't have to be difficult."

In recent years Carroll has found the perfect musical partner for her spirited new Irish music in Doyle, a former member of the band Solas. The Dublin-born guitarist is a brilliant accompanist, combining harmonic richness with dazzling agility and speed. He also helped arrange the 23 Carroll-penned tunes on 2005's In Play, the duo's first release.

"I have my own idea of what I want the chords to be," Carroll says. "But when John starts playing and putting in his ideas, the tune gets better–a lot better. Being fast also means he gets things fast. He really understands those gutsy kind of tunes that are about 'Let's dig in here.' And if you do something new with a tune, if you change something, he'll pick up on it right away and throw it back at you with a laugh the next time it's played through."

In other words, he'd be a great guy to have at a session.

Liz Carroll and John Doyle appear at the Vancouver Folk Music Festival on Saturday and Sunday (July 14 and 15).