Sometimes they sounded like a single fiddler. More often, husband-and-wife team Natalie MacMaster and Donnell Leahy tossed tunes back and forth like a hot potato, harmonizing to the other's music and letting the differences in their styles shine through.

Both fiddlers are renowed on the international stage. MacMaster often headlines with her own touring band, while Leahy leads Leahy, a family band made up of his talented siblings.

But Sunday night in Long's Park, in Lancaster, Pa., the two were sharing the stage in a rare double bill.

Backstage after the show, MacMaster and Leahy said it's still a challenge to combine their music into a single performance.

"It's harder than you would expect," Leahy said. "But we play different styles. If we put a tune together, we play it different and ... what happens is we mask each other's qualities." Besides, MacMaster said, "just to play a melody together is not necessarily as flattering as you might think."

MacMaster is firmly grounded in the Cape Breton styles, which developed from Scottish immigrants who settled on Canada's Atlantic Coast. Leahy comes from a more Irish background, mixed with Quebecois, Cape Breton and European influences.

"We grew up playing music by ear," Leahy said. "You can't help but pick up a few things. You hear things, and they appear in your music."

They've been married six years and have two young children together, but they're still a little timid when playing together, Leahy said, because neither wants to take the limelight away from the other.

Usually they take turns at melodies or harmonize to one another. "Or we write a new tune and learn it together from the ground up," Leahy said.

"We both love music," MacMaster said. "Sometimes it's a grind, but when you put it together and get past those humps, it's a complete joy."

Another challenge is having two young children in the house, MacMaster added.

"Sometimes we'll have a babysitter in our home for four days, just so we can practice," she said. "We have to take our music home with us. That's how we put a show together, that's how we practice, that's how we write, that's how we do everything."

Of course, conventional wisdom is that the children of Leahy and MacMaster will either grow up to be amazing fiddlers themselves, or else they'll rebel against music and become doctors or lawyers. The proud, doting parents prefer not to set too many expectations.

"I expect they're going to play instruments. That's just the culture we live in," Leahy said.

"But we will be pushing music," MacMaster chimed in. "There's no doubt about it."

"I want them to understand and appreciate music," she explained. "As adults, I want them to be able to receive from music all the things that I have. And if they have a talent, we will certainly encourage it. If they don't like it and their talents lie elsewhere, then it's our job as parents to help them find it."