THERE are big laughs at the end of the phone. Violinist Rachel Podger, if you can pin her down, is a bright spark. On the day we’re due to speak she has six hours of train travel on various branch lines: she lives in Brecon, a village in the Welsh hills whose charms don’t include speedy access. That plan is scuppered when the bridge of her violin collapses and takes the finger board down with it. It’s the kind of instrument crisis that would panic most touring musicians, let alone one about to direct her own group for the first time at the Edinburgh International Festival. A few days later Podger is cheerfully telling me about her genius luthier in Ludlow. “The calmest man in the world,” she says. “He just exudes reassuring vibes. Fiddle sounds great now. Better than before!”

Podger comes to Edinburgh this week with Brecon Baroque, the group of old friends and former students whom she brought together formally in 2007. “After years and years of playing with other ensembles I was definitely ready to have my own,” she says, heavy stress on the "definitely". She grew up in baroque ensembles, quite literally, with both parents singing in John Eliot Gardiner’s Monteverdi Choir in the early 1970s. She herself has been a regular guest leader of the world’s top period-instrument orchestras, including the Orchestra of the Age of Enlightenment, the Academy of Ancient Music and the European Union Baroque Orchestra. She knows about the dynamics of working with somebody else’s band.

Eventually it was going rural that did the trick. In the early 2000s she and her partner Tim Cronin – also a string player and teacher – settled with their children in Brecon and were asked to take over programming of the local early music festival. “So there was this open door,” she recalls, “and I went for it. I asked all the people I most wanted to work with. Pretty simply formula, I guess.” The couple soon turned Brecon’s annual October music series into a real musicians’ festival, small in scale but ambitious in musical scope and calibre.

At the core of the festival is a resident ensemble that includes violinist Johannes Pramsohler, violist Jane Rogers, cellist Alison McGillivray, harpsichordist Marcin Swiatkiewicz and lutenist Daniele Caminiti. They are charismatic, bold-thinking musicians – kindred spirits playing repertoire they like with people they like. Try their recording of Vivaldi’s L’Estro Armonico concertos. “The blithe twists and technical pizzazz are feisty and spontaneous,” I enthused in The Herald when I chose the disc as one of my favourite albums of 2015. “There’s no sense of hierarchy here, but a real feeling of everyone mucking in and genuinely enjoying themselves.”

Podger says she honed in on these particular players “because … well, wavelength. A lot of us studied at similar periods. We know each other from a grassroots time when there was really deep musical and emotional forming going on. Also, everyone is self-sufficient in their own right as a musician, a lot of them as directors of their own groups. To get that quality of people together … it’s really vibrant. Exciting. It is chamber music. When you play with like-minded people, you don’t have to discuss much. There is masses of give and take but you can still be true to yourself.”

Tomorrow’s Brecon Baroque concert at EIF is a bit of an oddity. There are two works on the programme, both by Mozart – but not quite. We’ll hear his brooding G minor String Quintet and his exuberant Sinfonia concertante for violin and viola, except the latter is in an obscure arrangement from 1807 that reworks the solo parts and orchestral wind lines and shares them out among a string sextet. The choice, unsurprisingly, didn’t come from Podger but from the festival. “They were very clear about what they wanted,” she says. “No, I’ve never played this arrangement before. It’s really quite strange. We don’t even know the name of the arranger.”

For a musician who devotes her professional life to investigating the most authentic ways of playing baroque music, the notion of playing a Mozart cover version might seem nonsensical. These kind of arrangements were common enough in the early 19th century, designed to sell sheet music to wealthy music fans in Vienna who would gather friends in their drawing rooms and spend an evening reading through the big hits of the day. “I supposed the basic fact that this one survived is what makes it interesting,” Podger ventures.

She knows the original version of the Sinfonia concertante intimately – she has performed it umpteen times. What does it feel like to play Mozart’s music via someone else’s notes? “Pretty weird!” she admits. “But then, it has taken on its own life. I’ve come round to it,” she adds. “Genuinely I have! The wind parts are integrated in way that is actually quite colourful. There is a certain amount of bravura in the arrangement that makes it fun to play. Everyone gets a shot at the solo lines, so in a sense it’s perfect for a group of big personalities like ours.” ?“And the whole historically informed performance thing…” she pauses. “In a way, we’re approaching this with more flexibility because we know it’s an arrangement. But we’re also thinking through what was fashionable at the time, and considering this as a period piece from 1807. The players in that Viennese drawing room would have known the original for sure – it had only been published at the beginning of the 19th century – so the thing we need to do is to get into their way of thinking. There are loads of slurs, for example, which is a very early 19th century Viennese thing. It makes me cringe a bit when I think about doing those kind of slurs to Mozart, but I need to get over that.”

Will this project open the floodgates? Will she be programming Stokowski mega-orchestrations of Bach organ fugues next? That big laugh again. “Nah. I tend to go for the source. There was a feeling when I started this project that I didn’t want to do it that way, that I wanted to do it Mozart’s way. But I’ve enjoyed pondering questions around flexibility. It speaks of a time not like ours. Today we think, ‘dead composer, don’t touch it’. There is room for that, and don’t worry, I’m not about to jump ship from the historically informed movement! But it’s also OK to embrace a more fluid mentality. I think!”

Rachel Podger directs Mozart Arranged at St Cecilia’s Hall, Edinburgh, tomorrow