Arts: A night to remember

I think it's really sensuous ... You can almost eat it. When I first heard it live I just thought, `what a sound' - it almost knocks you out." The sound, by which the composer Mark-Anthony Turnage has been seriously seduced, belongs to the classical/baroque Orchestra of the Age of Enlightenment. Not the type of musicians with whom the cutting-edge Turnage is used to working at all, in fact.

But the BBC's idea of combining old and new, to demonstrate how the orchestra has changed and developed across the centuries, didn't stop at juxtaposing works by Beethoven and Turnage or Haydn and Oliver Knussen. Why not intertwine two contrasting ensembles, the Orchestra of the Age of Enlightenment (OAE) and Birmingham Contemporary Music Group (BCMG)?

Both are bands with which Sir Simon Rattle, who is to conduct this special BBC Millennium Concert, is closely associated. And the two orchestras, which perform at different pitches, wouldn't just meet at the interval but would actually play together at the same time. On Sunday night the 20 members of BCMG will tune to the present-day standard of concert-pitch in which the oboe's traditional tuning call of the A above middle C has 440 (double) vibrations per second (44 Hz).

The 32 OAE musicians, on the other hand, sticklers for historical accuracy in the "authentic" performance practice that composers such as Mozart, Haydn and Beethoven would have recognised, will stick firmly to their principles and tune to 430. And at roughly a quarter of a tone apart, the two ensembles will stay, at least as long as the temperature in Ely Cathedral doesn't drop or, less likely, even with the presence of television cameras, rise dramatically. It's an extraordinary idea and one which has proved a learning curve for all concerned, not least Turnage, commissioned to write the new collaborative work.

"I began About Time when I was in Japan and felt strangely unsettled and disturbed by a mini-earthquake that occurred during my visit. The inspiration, or rather the actual music, actually came to me in a dream. Nothing like that has ever happened to me before or since.

"I only heard the OAE live for the first time after I'd agreed to write for the two different groups. I heard Frans Bruggen conduct Mozart with a fortepiano and though I'm honestly not a big Mozart fan, it sounded fantastic. At first I wrote a piece with very straightforward parts for the OAE, all simple tonal triadic music. I've known BCMG for a long time but composing for the OAE felt riskier, and I realise now I didn't entirely trust them, which was my mistake. I tried to chicken out or else get the OAE to tune up to standard concert pitch but that wasn't too popular ..."

To complicate matters, at an early run-through, the BCMG musicians sounded louder, their tuning more dominant and the effect of their higher pitch more brilliant to those accustomed to it. The piece needed more contrast and Rattle suggested to Turnage that perhaps he'd underused the period players and that he should be more positive, forget the tuning and just compose. "Bless him for taking it on ... It's thrilling and risky and sounds absolutely gorgeous," says Rattle.

Now the two sides have been given material in which they actively respond to each other, first in small interchanges and later in long-held contrasted chords which alternate between early strings and the contemporary group. These merge into glissando effects where players from both groups meet each other in a common pitch, with "past" and "present" mingling at first almost warily and then more vigorously.

Turnage enjoyed having room to expand, "I like the idea of both pitches playing together, not just in contrast. And I thought I'd do it at the end of the piece because it's like everyone coming together." One work for two quite separate ensembles playing instruments of totally different periods, each in their own performing style and clinging to their own pitch, would be quite enough for most composers. But Turnage has added a third dimension.

"I went to Ely Cathedral and when I saw the Octagon I just couldn't resist the spatial opportunities offered by an offstage brass quartet." So two trombonists and two flugel horn-players from BCMG will be perched high above the Cathedral crossing in the stone Octagon with its wood lantern, the Gothic equivalent of the Classical dome and one of the wonders of English cathedral architecture. Like the sudden sensation of space brought about by the contrast between the shadowy vaulting and bright light flooding on the star of the Octagon, About Time will begin with a distant evocation of the breaking of day, represented in a simple five-note theme that is never far away throughout the piece. The austere Cathedral's resonant acoustic combined with the quartet's lofty position is likely to produce yet another difference in pitch.

As the first composer to confront the problem of creating such an unusual work (it lasts about 12 minutes), Turnage didn't expect many organisations to consider taking it up although he tried not to create a piece locked in to one performance base. Yet even before its premiere there's already been a lot of interest. "I think people want novelty," suggests Turnage, who has found the whole experience "incredibly hard," and remains worried that the effect might be closer to an out-of-tune school orchestra than musicians from two highly regarded professional bodies. He'd be grateful, I'm sure, if you'd kindly leave your tuning-fork at home for this concert.

Sir Simon Rattle conducts the BBC's Millennium Concert, which includes Haydn's Te Deum, Oliver Knussen's Two Organa and Beethoven's Choral Symphony, live on BBC2 and Radio 3 on Sunday 12 Dec at 8.00pm.