'Beethoven was always too much. He's not slightly anything, he's very everything ... It takes its toll. Preparing this music, conducting it, playing it, you feel yourself stretched on some kind of psychological rack'

With five down and four to go, Edward Seckerson listens in as Sir Simon Rattle prepares to complete his first Beethoven symphony cycle

They're the ultimate challenge for every conductor - the works by which reputations are made or broken in the concert hall. The Beethoven Nine. At once the most familiar and yet the least knowable scores in the entire symphonic repertoire, both the bedrock and the pinnacle of the whole western tradition. Every maestro must measure up against them: Furtwangler, Klemperer, Karajan in the past, Norrington, Gardiner, Harnoncourt in our own day - all have scaled their heights. Now Sir Simon Rattle has begun the ascent. And about time too. After a decade and a half in charge of the CBSO, Rattle is far and away the longest serving music director of any major orchestra. He's conducted everything from Mozart to Mahler, everyone from the period players of the OAE to the sheeny strings of the Berlin Philharmonic. But he's never yet tried his hand at a complete Beethoven cycle. Until now.

"With the help of assiduous labour you shall receive Mozart's spirit from Haydn's hands." Count Waldstein to Ludwig van Beethoven, patron to protege. No doubt his famous remark was well-intentioned, well-meaning, offered in a spirit of optimism and encouragement. What are patrons for, if not to patronise? But little did he know. Waldstein had heard the future, invested in it, but he could have had no conception of the return.

It was to be a further eight years before Beethoven went public with his First Symphony. And he wasn't about to receive anything from Haydn's hands. Take, yes; snatch, seize and transform; reinvent. The Second Symphony was perhaps the last point at which Haydn could make any real sense of where Beethoven's music was going. That's a Haydn symphony fit to burst. The Third, the "Eroica" - one of only a handful of works truly to change the course of musical history - was forged from the will to live in the face of a desire to die: music of spiritual necessity, defiant, intransigent, tragic and comic, human and divine, sublime and ridiculous, inevitable and ineffable. Revolutionary music for a revolutionary age. And ever after. "Es muss sein," said Beethoven: "It must be."

Sir Simon Rattle is presently contemplating the wider implications of those three little words. Sooner or later, they all do - the great and the good, the not so good. This is one rite of passage that comes to them all: a first complete cycle of the Beethoven Symphonies. In Birmingham, in London, and - in the course of one daunting week in November - in Frankfurt, Rattle will reveal all - and more - of himself. He is weary, elated, anxious, more than a little awed. But ready.

Let's put it into perspective. Last summer, he and the City of Birmingham Symphony Orchestra set down 53 pieces of contemporary music in seven days for a new Channel 4 TV series. But even that was as nothing, but nothing, he says, compared to the challenge, the responsibility, of Beethoven's Nine. When the most celebrated, the most revered, the most played symphonies in musical literature beckon, conductors prepare to be judged and found wanting. You may have earned the right to try, and even fail, but nowhere are a conductor's shortcomings, a conductor's mistakes so audible as they are here. As Rattle himself says: "There is simply nowhere to hide."

"This music is merciless. Beethoven is the clearest mirror that we have. He tells you exactly where you are in every sense - musically, spiritually, rhythmically, in terms of the imagination. Look, even Goethe shied away from Beethoven's presence. He couldn't take it. It wasn't just that they were so different, that Beethoven was eccentric and Goethe patrician - it was this stunning honesty and directness. It was inescapable, it made people very, very uncomfortable. Remember that the person closest to Beethoven - his nephew Carl - tried to commit suicide in an attempt to break free of his influence. I mean, when Beethoven's brother died, he basically kidnapped Carl. And Carl simply couldn't take it, this smothering, suffocating, overpowering presence.

"Beethoven was always too much. He's not slightly anything, he's very everything. The drama is very extreme; so is the humour. Suddenly, I'm grateful for all the Mahler I've conducted. It's these amazing contradictions - from suicidal to witty within a bar. But it takes its toll. Preparing this music, conducting it, playing it, you feel yourself stretched on some kind of psychological rack."

It is two o'clock on a Monday afternoon when everything is a bit of a stretch. Rattle and his orchestra are limbering up for a first rehearsal of the Fourth Symphony. No fine detail as yet. This first few minutes is for loosening the fingers, elevating the pulse-rate. We are coming out of the slow introduction - Rattle offers a running commentary over the music, a few preliminary pointers: "Think of these chords as long shadows," he tells his strings; "very little vibrato... and winds, no beginnings to your chords... take them out of the air, pale and mysterious... Now firsts, lean into that G-flat just a shade" - the intensity is building now towards the allegro vivace - he is shouting now over the crescendo - "Reach... reach... reach... but save something for the fortissimo... yes, HERE" - and they're off the blocks into the sprint.

So much for the warm-up. Now detail. God is in the detail. "Can I deliver my yearly lecture on the placing of the first chord? Strings, wait until you actually hear the wind chord before you play your pizzicato - it should literally drip off the end of the wind chord..." The late Herbert von Karajan taught him that little trick. So you see, something valid can be drawn from the shadows of former times - discredited times?

Actually, Rattle doesn't see it like that. He sees himself in the very privileged position of having come to this music via Mozart and Haydn - and that in itself by design, not chance - from a generation of musicians whose good fortune stems almost entirely from the benefits of hindsight. "Any thinking musician of my generation cannot help but be a product of the gigantic flux of performing styles which have informed the last 40 years..."

The great inspirational "traditionalists" of the post-Wagnerian era, like Furtwangler and Klemperer and Karajan, and now the radical "back- to-basics-with-hindsight" revelations of period performance practitioners as diverse as Norrington, Gardiner and Harnoncourt - Rattle has drawn something from them all. But in the small hours when he is alone with just his thoughts, his instincts, his scores, the most important thing to remember is not to remember. The remembrance of things past - remembered interpretation, remembered emotion - is a real problem for young musicians tackling core-repertoire today.

So each performance is a first performance. Nothing can be taken on trust. And Rattle's considerable international reputation (the world continues to squabble over his available dates) is founded entirely upon his ability - his genius - for doing just that. We've heard and yet not heard these great works. With Beethoven, the shock of newness must prevail, each and every time.

"No one is pretending that we are playing Beethoven's music the way he would have heard it..." But might we be playing his music the way he would like to have heard it? "I know what you're getting at. But it doesn't quite follow. Having worked with period instruments, we know what they will do naturally. The fact that Beethoven wanted something more than the instruments will do naturally does not necessarily stretch all the way to saying that he wanted what a symphony orchestra in the 1960s would have played. Because there are problems with notation for a start. The same notation meant different things in different times. Note values were entirely different: the whole concept of sostenuto - 'sustaining' - was different. So you have to evolve an understanding of all the expressive 'grammar' of the time - the pronunciation of this music - and how best to apply it now. So I will say to players: always think in terms of one strong beat and two lighter beats.

"Almost the most important thing we've learnt from period performance of this music is the idea of 'pronouncing'. Phrases must begin. It's like words: you never say 'Bee-tho-ven' - it's ungrammatical. So that's fundamental. Then there's vibrato: I say, think of it as an effect, an adornment, not the norm; think of sforzandos as expressive and forte-pianos as really sudden, and staccatos as not necessarily short. I think Beethoven means dissonances to be more stressed than consonances - it's the shock tactician in him. So there's your basic vocabulary to be taken and fashioned into sentences, paragraphs, chapters..."

On this particular Monday afternoon, it's very much a word-by-word process. The rehearsal makes haste slowly. "A lot of what we are achieving here with bowings is good - it just takes a lot of Weetabix. Remember, fiddles, as we start the allegro vivace, those little grace-note flourishes should be crisp like castanets..." And Rattle works painstakingly with his players on how best to achieve precisely that articulation. Much is implicit in Beethoven's phrase markings (staggeringly, there is still no published urtext of the Beethoven Symphonies incorporating all the latest research on extant sources: Jonathan Del Mar's edition, used now by Rattle and others, should be urgently recognised as such).

The slow movement brings different problems: "Where the most pain is, we need the least vibrato," he tells his strings - an eloquent note, achieving eloquent results. Likewise in the rumbustious finale, with its busily subversive figurations: "Think of them as a rumour..." Rattle's way with words makes music. It's never just about the notes but about the reasons for them, he reminds his players, recalling something Kurt Sanderling once said to the Los Angeles Philharmonic while preparing the Ninth Symphony: "I don't care that you play together and in tune, because unless you understand that this sound is praying for mercy, you will not get the right expression." And expression is communication, conductor to orchestra, orchestra to audience. Watch Rattle in performance. There's a reason for every gesture: you really do hear what you see. If you see him cue, coax, cajole a player or group of players, you can be sure that what you hear will illuminate, intensify the musical image. The black magic is all in the balance and the phrasing and, finally, the characterisation.

Robert Schumann once described Beethoven's Fourth Symphony as "a slender Greek maiden between two Nordic giants" (namely the Third and Fifth Symphonies). But the Fourth according to Rattle is neither slender nor maidenly. Any more than the Eighth is merely jocular. How perceptions of great art change. At the turn of the century, there were still those for whom Mozart's G minor Symphony (No 40) was "charming and rococo". Which begs another question. Are we now better placed, better distanced, to view these works objectively, to see them as they really are? Or are our perceptions still coloured by the times in which we live?

"Well, I suppose it's inevitable that we are still looking for things that confirm the way we feel at the end of the 20th century. So we will tend to see more darkness than even Beethoven will have seen. Where people of his time will have heard only affirmation, we might now hear fragmentation and doubt. And yet it still holds true that most of Beethoven is a journey through from doubt to affirmation - culminating, of course, in the Ninth."

The Ninth. If ever a work began groping in the darkness, this is it. Where does it begin? Does it begin? Long before we hear anything, that's for sure. "That opening," says Rattle, "is a real beginning-of-the-universe moment... that whole first movement is like those paintings of Van Gogh where he started painting on the frame or even the wall, as though the canvas couldn't contain the work..." And this is the moment when Rattle brings on the full might of the modern orchestra with double winds, not for weight but for "relays", so physically taxing is the piece. He's also ready to adjust the size of his band (as Beethoven surely did) according to the size of venue he's playing. Now that's what I call historically well-informed thinking.

Rattle still maintains that he didn't fully grasp the Ninth - and particularly the choral finale, so used and abused in all manner of contemporary connotations - until he saw Part 2 of Goethe's Faust as realised by Simon Callow some years ago. "It's the surreal lunacy, the innocence of it. It's that kind of joy, not some grand, monumental, banner-waving triumph. Like the Pastoral symphony, it's the grandson of Haydn's Creation, only the vision is that of a more troubled soul. It's got the gravediggers, too." And it's got the lowest note possible on the contra-bassoon: "a celestial passing of wind," Rattle calls it. Editors of the day thought it wasn't playable, so they changed it. Along with much else. Again, all credit to Jonathan Del Mar's diligence.

It's at times like this that conductors talk of taking journeys and climbing mountains. Rattle is more specific. "It's K2, isn't it? Right now, it's quite hard to see beyond it." But he will. On the horizon is Wagner, the man who so wanted to re-compose Beethoven in his own image. When you're through climbing mountains, you go in search of the Holy Grail. Parsifal. Amsterdam, 1997. Now there's a date for the diary.

Rattle conducts Beethoven Symphonies: Nos 6 & 7 Birmingham Symphony Hall Tuesday, Barbican Friday; Nos 8 & 9 Birmingham 25 Oct, Barbican 27 Oct. Booking: Birmingham 0121-212 3333; London 0171-638 8891