Some ideas are so good they have an existence that is independent of their execution. For example, someone thought it would be a good idea to screen an iconic silent horror movie in a spooky chapel, and get some bloke to play the organ as the soundtrack.

Simple. In fact, do you really need to be there? Now I've told you what was involved, you can probably imagine the whole thing. And, in this case, you would be dead right.

Actually, when I first saw the notice for David Bednall accompanying the screening of the 1922 German horror classic Nosferatu in Keble College Chapel, a nameless dread crept over me. It was every bit as chilling as Max Schreck's famous evocation of the archetypal vampire.

For the notice contained the dread word: improvisation.

Now don't get me wrong. I love improvisation. I'm a Grateful Dead fan, a jazz lover and a Derek Bailey disciple. I've also absorbed enough about the traditions of the King of Instruments to know that Bach was a great improviser.

The trouble is, improvisation very often means weird. The dread that gripped my soul was that I would go in search of Gothic majesty and be presented with a crash of atonal art music that ruined the movie and dishonoured the setting.

Still, I went. And I should have had more faith.

David Bednall, currently the organist at Bristol University, and a noted composer and improviser, began by exhorting us to watch the film rather than take particular notice of his playing, and we all did as we were told.

As a result, we were treated to a captivating cinematic experience, with musician and director bonding across 90 years to bring us 100 minutes of glorious audio-visual expression.

David Bednall wrung every last drop of Gothicness (Gothicity?) from the film, with highlights that included bits of Wagner, a witty quotation of 'Morning' from Grieg’s Peer Gynt Suite as the dawn broke in Transylvania, and a 'Jaws'-like sequence when the carnivorous plants were gobbling up hapless insects.

But the truly unforgettable moment was the one we'd all hoped to see, from the instant the idea of Nosferatu in a grand chapel, with a grand organ, came our way.

It was the bit where the Count himself is revealed framed in the Gothically arching doorway of the hero's bedroom at the castle.

What you want is a massive, doom-laden, stops-to-the-max chord with teeth-juddering bass, that goes on for ages until you start to wonder how good the chapel's architects were, and might you meet a historic end, buried by a surfeit of Gothic romance?

And that's exactly what we got. It was deliciously clichéd, perfectly timed, and utterly terrifying. I'll have to sleep with the light on for a few more days yet.

If only F.W. Murnau, the director, could have been there. He would have embraced David Bednall as a fellow visionary, and they would have revelled together in the eternal connection of a magnificent idea.

Organist and composer David Bednall’s improvised score for Nosferatu is part of a long tradition. Nosferatu is one of the first ‘cult’ films. Its near death at the litigious hands of the Stoker estate and consequent rarity up until the reconstruction work of recent years, coupled with sinister (if probably entirely apocryphal) stories of the mystery surrounding Max Schreck and his portrayal of Count Orlok has allowed its eerie air to permeate beyond the film itself.

This sense of the uncanny has inspired many musicians to use electronic effects and discordance to create something genuinely unsettling to a modern audience, or to echo the more avant-garde, atonal music of the film’s own time. What little we have of Erdmann’s original orchestral score suggests that this was not the intended direction - it’s firmly rooted in the romantic rather than modernist tradition.

Bednall’s improvisation cleaves closely to this - as one would expect from a composer who has a self-confessed affiliation to more traditional forms of polytonality and the later romantic composers. His lush chords heightened the intensity of the film - which is, at base, a melodrama of striking images and - in the absence of a defined technique of film acting - big, theatrical performances.

We can’t, alas, be a 1920s audience, and it needs to be acknowledged that the unformed nature of film’s narrative grammar at the time creates difficulties for the modern viewer. In particular, early film makers couldn’t casually rely on audiences understanding the visual shortcuts we now take for granted. Murnau’s unnerring visual instinct carries us through most of this - you’re never far away from the next astonishing short - but we are still faced occasionally with unnecessary longeurs and an over-reliance on text narration and expository dialogue to clarify the story.

This is where Bednall’s improvisation falls down somewhat. After some early experiments with the organ’s capacity for infrasound and sudden dynamic changes, his playing just seemed to build and build. In these slower scenes his huge, dense chords occasionally seemed to have nowhere to take themselves and tilted towards sludginess.

This was only noticeable in parts, however, and in the main this was a sensitive - even witty - response to the film that was clearly rooted in an understanding for, and admiration of, its dynamics. And, of course, one should take any excuse to enjoy Murnau’s indelible classic of early cinema.