It's two in the morning, and a double-bass player from one of Europe's leading period-instrument orchestras is laying down a jazz groove that, along with the drums, has his enthusiastic audience dancing under the stars. His partners in this amiably ragged vamp comprise a student from the local music academy on piano and no less a figure than the region's deputy prefect on trumpet. Six hours previously, all were intent on music of a very different kind - a Mass setting by one of the masters of Renaissance counterpoint, given in a performance of sublime majesty and technical expertise.
As the band improvises late into the night, the chatter of voices bounces off the stunning Romanesque façade of the 11th-century abbey church and the variegated white stone walls of its starker 17th-century nunnery buildings, revealing the origins of the people assembled here: French predominates, but gathered round tables laden with wine and fine brandy are clusters of people speaking German, Italian, Dutch, Flemish and, of course, English.
Every music festival, from Verbier high in the Alps to St Magnus in the Orkneys, from glitzy Salzburg to the egalitarian Proms, can lay claim to its own particular magic. But it's doubtful you'll find anywhere quite like the Académies Musicales in Saintes, an otherwise sleepy town in the heart of cognac country some 50 miles inland of La Rochelle in south-west France. It's a place where musicians, critics and audience are permanently engaged in spirited conversation, from dissections of last night's concert to anticipations of tomorrow's revelations. One moment you can be sitting in the audience behind that pioneer of early music Gustav Leonhardt; the next you're sharing a bottle or two of Bordeaux with musicians from the resident band, the Orchestre des Champs Elysées. And though the late-night revelry might indicate otherwise, there can be no doubting that this gathering is dedicated to one thing: music performance of the very highest standard.
The brainchild of Philippe Herreweghe, the Belgian maestro who trained as a doctor but who now ranks as one of the world's leading period-instrument conductors, the Académies Musicales has been attracting the most accomplished musicians to its intoxicating shindigs for 31 years now. It's a small affair, limited by the 650-capacity of its central venue, the Abbaye aux Dames, and its audience is largely made up of musicians and hard-core enthusiasts, though the festival's general secretary, Odile Pradem-Faure, is keen to point out that some 25 per cent of the audience is drawn from local people. Though it was originally set up exclusively as an early music festival, Saintes has followed Herreweghe's interest in broadening his period-instrument explorations to include the Classical and Romantic repertoire. This summer, that meant two 19th-century giants getting the Herreweghe treatment - Brahms's Deutsches Requiem and Bruckner's Seventh Symphony.
But the festival never strays far from its early-music roots. Bach has long been a staple, with performances this year including the G major Mass, set against Stravinsky's own starkly modernist Mass. This juxtaposition of ancient and modern is something that Stephan Maciejewski is particularly proud of having introduced to the festival, first as its artistic adviser and now as the inheritor of Herreweghe's mantle as artistic director. "We started in 1988 with a series of concerts in which we put Luciano Berio's eight Sequenzas alongside Bach cantatas," he says. "At first, our public was wary, but now they're used to such an approach. In some ways, what we're doing is presenting 500 years' worth of contemporary music. When the music - whether it's Orlando de Lassus or Stravinsky - is so inventive and modern-sounding, it stays that way forever. Renaissance music is so old that it's actually contemporary."
Indeed, the concerts I caught during the latter half of the 10-day festival confirmed Maciejewski's theory. Paul Van Nevel's Huelgas Ensemble sang Cipriano de Rore madrigals and his Missa Praeter rerum seriem with infinite precision and delicacy, while Pedro Memelsdorff and his vocal/ instrumental group Mala Punica offered a fascinating recital of 14th-century courtly songs from Castile. (Both ensembles appear at the South Bank's Early Music Festival next month.) Perhaps most extraordinary of all was La Venexiana's recital of madrigals by Carlo Gesualdo, impeccable accounts of daringly avant-garde works that fully justified Maciejewski's claims about the shock of the old.
But it was when Herreweghe was present that Saintes was most abuzz with anticipation. He remains closely tied to the festival, each year conducting six or so concerts. Earlier events had seen him directing Mozart and Bach, as well as the Jeune Orchestre Atlantique, whose players are drawn from the 60 students taught at Saintes' Centre Culturel de Rencontre. The centre recruits the finest players from Europe's conservatoires and, uniquely when all the music schools concentrate on Baroque instruments, trains them in the very precise needs of the Classical/ Romantic practice. The students' two concerts, first Mendelssohn and Schubert and then a triumphant triptych of Mozart, Haydn and Beethoven, gave evidence of why the centre's reputation for musical excellence is so high that its 12-part course will, as of next year, be counted towards the final exam of the Paris Conservatoire.
It was the promise of Herreweghe's handling of Brahms and Bruckner, however, that had Saintes most excited and drew the critics down from Paris. If there were any worries that Bruckner's Seventh might swamp the small Abbaye aux Dames, they were instantly dispelled by Herreweghe's careful dynamic control, which fully exploited the marvellous textures of the orchestra's period winds and gut strings. Even the mighty brass - complete with Wagner tubas, for added punch - was sensitively handled, the natural horns a vital component of an organic vision that strips the symphony of any hint of bombast and infuses it with aching intensity.
Herreweghe, at 56 still excited by his voyage of discovery, explains that Saintes is something of an experimental laboratory, allowing his Orchestre des Champs Elysées to discover new facets of the Romantic repertoire before taking the results round Europe's concert halls and committing them to disc. "The most important thing period instruments can bring - to Bach as much as Bruckner - is colour," he says. "In Bruckner, especially, we can articulate phrases in a much more subtle way than a 'modern' orchestra does. And as soon as you use this approach, everything becomes more translucent; Bruckner suddenly becomes much less aggressive and hard, an approach that brings him closer to Schubert. This is the music of a very sad man, a broken man, a man who is lonely and missing God. His big, loud chords are not a sign of power, of German might, as some interpretations represent them, but of deep inner pain. I want to strip Bruckner of all the Nazification he has suffered." The groundbreaking conductor will continue his exploration of Bruckner's symphonies next year, and has plans to record them for Harmonia Mundi.
Herreweghe also brought this questing approach to the closing concert, an all-engulfing account of Brahms's Deutsches Requiem. The soloists - the English soprano Katharine Fuge and the German baritone Dietrich Henschel (who had astonished everyone the night before with the dramatic intensity of his recital of lieder by Wolf, Korngold and Mahler) - play a relatively minor role in Brahms's masterpiece, whose success largely rests on the efforts of orchestra and chorus. Herreweghe's meticulous phrasing and tonal detail let the orchestral colours glow with burnished warmth. His chorus, a festival choir assembled around the crack Collegium Vocale Gent, just occasionally displayed the need for tighter control, but more than made up for minor shortcomings with superb vocal purity and dynamic range. Again and again, one was struck by how Brahms's writing harks back to the great German choral tradition arching from Schütz to Bach, while being excited anew by how he seamlessly marries this to ripely romantic phrasing and tone painting.
And if you thought period-instrument Bruckner was pushing at the boundaries, then what about Mahler? The orchestra's instruments, of course, are not strictly "period" for the early 20th-century Viennese soundworld of Mahler. But Herreweghe couldn't miss the opportunity of using Henschel - a singer who manages to get inside the music to an almost unnerving degree - in the last of the Rückert Lieder, "Ich bin der Welt abhanden gekommen" ("I have lost track of the world"), a song in which the composer breaks through barriers to explore new means of expression. The baritone had everyone captivated from the start, but it was the sheer beauty of the orchestral sound, enhanced by the mellow richness of period winds and strings, that truly took the breath away.
But then, making new discoveries is what Saintes is all about.
The Académies Musicales de Saintes next takes place 14-25 July 2004 (00 33 054 695 9450; www.festival-saintes.org). Ryanair flies daily from Stansted to La Rochelle and Poitiers