In 1846, the composer Hector Berlioz presided over a catastrophe: the world-premiere performances of his so-called dramatic legend, The Damnation of Faust. He could have handled it better if his audiences had hated the piece and vilified him for it. But the audiences had voted with their feet.

On a freezing opening night, the Opera Comique in Paris was half-empty. They simply didn't turn up. The second performance, two weeks later, fared no better.

A third scheduled performance was cancelled.

Berlioz was crushed. He had invested massively in getting his new Faust - one of the most blindingly original, shockingly inventive compositions ever penned - on to the concert stage. It was his own promotion: he had booked the hall, the musicians and the singers, and done all the leg-work of administration, publicity and marketing. He had blitzed the press, and sent the libretto to the king and queen, requesting their attendance.

Getting Faust off the page and into performance cost him a fortune, and its tragic debut left him depressed and disillusioned to the point where he was given money by friends and supporters.He left Paris, quit France and headed for the more hospitable climes of Russia.

By all accounts, the first performance of Faust hadn't actually been that bad, though the tenor singing the title role confessed he couldn't understand his part; the bass singing the devilishly difficult and larger-than-death part of Mephistopheles could scarcely manage it; the orchestra players, although already experienced in playing Berlioz's supremely innovative music, were apparently in deep trouble; and the audience were completely at sea, not knowing if what they were hearing was an opera, a cantata or a musical mosaic.

Stephane Deneve, music director of the Royal Scottish National Orchestra, who will conduct performances of Faust in Perth and Glasgow this weekend, has no such doubts. He has a potentially strong cast, with the great mezzo Jennifer Larmore singing Marguerite, tenor Gregory Kunde as Faust and bass Nicolas Cavallier in the role to sell your soul for, as it were: Mephistopheles.

He is also quite satisfied in his own mind as to exactly what species of composition Faust is. "It's been staged as an opera many, many times since Berlioz's death in 1869, but Berlioz called it a dramatic legend', and to stage it as an opera goes against what is Berlioz's main idea. The Damnation of Faust is the world of the imagination," he says.

Deneve goes into great detail about why he believes Faust is inappropriate to the stage. The work is in four parts. There are 20 scenes, and some of these are very short, with massively abrupt cross-cutting and juxtaposition without transitions. The rate of turnover of events is dizzying. The apparent pace, other than in the more reflective and languorous scenes, is of a music that hurtles forward, relentlessly and inevitably charging to hell on a deliriously high-speed roller-coaster ride through experience.

"It's lightning-fast," says Deneve. "The movies could compete, but not the stage. But it's much richer just to use the imagination. And anyway, Berlioz specified it as a veritable opera without scenery or costumes'."

So what's Deneve's take on this phantasmagorical masterpiece, which sets Faust off on a trail of temptation from Hungary to Germany, to Marguerite's bedroom, and on to hell (no redemption in Berlioz's vision), where, in a cataclysmic climax, all the demons of Hades, the damned souls and the Prince of Darkness himself erupt from the bowels of the underworld, screeching in babbled syllables to the accompaniment of some of the most extraordinary orchestral writing ever imagined?

"This is unique music," says Deneve. "There is nothing like it. It's autobiographical. Faust is Berlioz. What spoke to Berlioz so clearly in the translation of Goethe that he read was the great loneliness of the artist. My main concern with this piece is that sense of loneliness: every part, or act, starts with aspirations, dreams or desires, and it always falls miserably. And I think that's what life is like for these big giants: they just dream, they hope, they idealise the world. And it always comes to nothing."

Maybe so - but en route to nothing, Berlioz has left us a riotously wonderful piece, packed full of dances, marches, choruses of every hue, funny music, outrageous music, subversive music, a disgustingly seedy, smoky pub scene, a song about a dead rat, vocal love music as ardent and passionate as anything in Puccini, and mind-blowingly fabulous music for the cynical, sardonic Mephistopheles, who pulls all the strings and really does have some of the best tunes.

"I actually feel that Faust and Mephistopheles are very close to each other, and Mephistopheles is a kind of shadow of Faust, a dark part of Faust," says Deneve.

Again and again, in our long conversation about this amazing, maverick masterpiece, he returns to the subject of Berlioz's astounding orchestration, once dismissed as loud, crude, lumpen and inept, but later realised as prophetic and light-years ahead of its time. Not for nothing has Berlioz been called the creator of the modern orchestra.

"He takes every possibility with the orchestra, as a painter would do, to make colours and mix colours to make any effect he needs. He knew everything, every nuance, about instrumentation. He knew all the possible emotional shades of the orchestra and every instrument in it.

"I don't like it when people criticise Berlioz for being a genius with no talent'. Everything he does is so inspired and so unique."

Behind all the flamboyance, stresses Deneve; behind the musical largesse and bigness, the self-publicity, the famous and quintessentially Romantic love affairs, "everything in his music is very seriously worked out".

But where does the stupendous originality come from? "I don't know. It comes from his mind, his genius - and the opium. You can hear that he's very sensitive to the effects and influences that existed in the opera, from Rameau to Weber" (a founding father of Romanticism).

"And Beethoven, of course, was a huge influence. So it doesn't come out of nowhere. But it comes out totally unique."

Nowhere is this more obvious than in the furious gallop of The Ride to the Abyss and the subsequent Pandemonium, where all hell, literally, breaks loose. "That music, at that moment, is totally crazy. It has the most incredible orchestration - it compares with the Witches' Sabbath in the Symphonie Fantastique - and you really feel that Berlioz must have been into a big, psychedelic, drug-addiction moment."

It's all fantasy, all visionary - but, feels Deneve, Berlioz makes it all real. The same is true of the great love music between Faust and Marguerite, when they finally get it together.

"It's such passionate intensity between them. It's full of meat, it's bloody, it's very Latin. The passion is very real; the emotion is always real. It's like a perfect movie with an amazing soundtrack."

The Damnation of Faust: Perth Concert Hall, Friday; Glasgow Royal Concert Hall, Saturday.