I have been asked, but have no real idea, about Jonathan Mills�s personal reactions to some of the mutterings and mumblings about his third programme as director of the Edinburgh International Festival.

I have been asked, but have no real idea, about Jonathan Mills's personal reactions to some of the mutterings and mumblings about his third programme as director of the Edinburgh International Festival, which opens next Friday.

Some of the mutterings have become explicit, none more so than reaction to his decision to launch the festival with a performance of Handel's oratorio Judas Maccabeus, written specifically to celebrate the Duke of Cumberland's thrashing of the Jacobites at Culloden. The issue, seen by some Scots as "a slap in the face", even gets into the new edition of the BBC Music magazine, with a terse comment from an SNP MSP.

But that's the surface. Many festival-goers are unhappy about the direction in which Mills is taking the EIF. One music addict said he reckoned it was "the worst festival programme I've seen in 25 years". Another, a senior arts manager, said: "There won't be much I'm going to this year."

Yet another, a retired director of one Scottish musical organisation, touched a raw nerve for many when he said he felt strongly that the core of the music programme ought to be a rock-solid orchestral series in the Usher Hall, whereas, over the past three festivals, the balance of the music programme has shifted elsewhere.

And then there is another issue for many pairs of ears: it's not just what you do, it's how you do it, referring specifically to the volume of what we used to call "period performance", which is a feature across the genres in Mills's music programme: orchestral, choral, chamber and operatic.

For the uninitiated, that refers to a style of performance which has developed over the past four decades or so. Crudely, the argument runs that we of an older generation who listened to the music of, say, Bach, Handel, Mozart, Beethoven and even beyond them, were hearing inaccurate and even corrupted accounts of their music.

We were hearing it on the wrong instruments wired with the wrong strings and played with the wrong bows, the wrong phrasing, the wrong articulation, the wrong slurs, the wrong speeds, the wrong expressivity, and so on.

What we were hearing, it was argued, was a re-imagining of what these composers intended, in terms of sound and meaning.

We were hearing relatively lush, plush versions of music that amounted to a total distortion of the original art.

Thus began the quest for authenticity. Out went modern instruments, designed to produce beautiful sounds with the power to fill large modern concert halls. Out went powerful metal strings on violins. Back came gut strings and baroque bows. Out went rich, expressive vibrato, which warmed and sustained the tone. Out went physical power and projection. In came lean, intimate chamber sonorities. Out went long, continuous phrasing. In came short, detached articulation.

They didn't even know what to call the revolution in the early days. It would be called "early music"; then "authentic performance", then "period performance" and, latterly, "historically informed performance".

We all remember the early days. It was excruciating, as players wrestled with reconstructions of historical instruments that they hadn't mastered, struggled to find and hold convincingly the right pitch and intonation, all the while fighting their ignorance and technical inexperience to try to establish a new order, backed by intensive musicological research that attempted to keep them on course and sustain their efforts.

Symphony orchestras laughed themselves silly, listeners recoiled in disbelief, critics cringed in embarrassment, and the rising modern chamber orchestras pursued their own all-consuming objectives while keeping a weather eye on the authentic brigade, perhaps sniffing potential.

We all know what happened. The movement grew up, established a new order, and began a process of converting music lovers on their journey towards taking over the world. And many of the best in the world will populate the music programme of this year's Edinburgh International Festival, where their staggering levels of virtuosity, precision, accuracy and passion should nail, once and for all, all those old prejudices.

Nonetheless, it is clear from comments received that there are many who still believe that the historically-informed mob are rarefied outfits playing niche music to an arcane, specialist audience. And here festival director Jonathan Mills takes serious issue.

"I think the moment has arrived when we don't any longer have to think of the Baroque as part of a specialist fringe activity," he says.

"About 25 or 30 years ago, when these ensembles were hooting and hissing and finding their own way towards absolute precision of performance, there was an element of fringe. That's long gone.

"With the plethora of ensembles, from the Orchestra of the Age of Enlightenment to the English Baroque Soloists to Chiara Banchini and the EU Baroque Orchestra, to Jordi Savall and Le Concert des Nations, there is a level, a standard now, that is superb; so much so that more conventional instrumental ensembles are finding it difficult to compete in that genre."

He cites particularly the Bach Collegium Japan, with its unique director Masaaki Suzuki, whose work Mills describes as "having the precision of a digital sculpture". And, surveying the calibre and status of all the groups in this field that he has invited to this year's festival, he underlines his thesis.

"The Edinburgh International Festival is a mighty mainstream festival. But this is now the new mainstream; it is not a tucked-away specialist early music festival."

Far from the mainstream in this year's music programme, however, lie The Caledonia Sessions, a set of four mid-evening concerts from David McGuinness's Concerto Caledonia, which proposes to get soil under its fingernails with a series of explorations of Scottish music from the eighteenth century and earlier, pulling in guest artists from across the genres, including Patsy Seddon, Michael Marra and tenor James Gilchrist.

The titles of the sessions are mouth-wateringly evocative: Triplepipes, Lust and Spilt Blood; Dance Band Night; Scotsmen on the Make; and Robert Burns's Worldly Friends. I have an instinct, knowing something of McGuinness's swashbuckling style, that this could be a smash hit.

Mills is very excited about it. "I am really itching to hear these sessions. I've asked David to put together four programmes that form very particular journeys: some are journeys with rituals, some with texts, some with biography, and some with history.

"Robert Burns is the elephant in the room. It's everybody except him, in a way; and that is quite deliberate. This is a kind of X-ray, an excavation to a place before, where we will perhaps hear less fully-formed traditions, something rawer, and perhaps rougher."

McGuinness is the perfect choice for this task, reckons Mills. "He is such a buccaneer. Some people are snarling up their noses at his presence, because everyone else was going to be reverential at a time when we've had all the reverence we need for Robert Burns.

"I wanted someone else to do something a bit left of field. But it is also to show that actually Burns and all those other people are connected to ideas that ranged beyond Scotland. This is not a domestic conversation. It was a sophisticated international conversation; it was then, and it still is now."

• The Edinburgh International Festival 09 opens with Handel's Judas Maccabaeus by the SCO and Festival Chorus under William Christie at the Usher Hall on Friday, August 14.

www.eif.co.uk