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I let Thomas Kräuter drive first. His surname is pronounced 'Kroyter'. His surname is pronounced 'Kroyter', and he's one of the car industry's many unsung heroes - a backroom wizard creating masterworks of engineering and not getting much credit for it.

There are hundreds like him, and they're happy to beaver away at the things they love, knowing they've got some of the best jobs imaginable. And what a job his is. He's the technical project leader on the Audi R8 V12 TDI Le Mans concept you see here, which - although this hasn't been confirmed officially - will soon become the greatest Audi road car of all.

"This is something new," says Thomas, as I motion him to take the driver's seat. He's been asked the same boring questions over and over by the stampede of journalists from all over the world who have decamped to Miami for a spin in this thing, so it was refreshing to do some driving instead.

I have other reasons for being happy riding shotgun. I don't want any distractions from the single aspect of this car I am most curious about - its sound. We're stepping into the unknown here, the first supercar of its kind. Much of it might seem 'normal'; it has a six-litre, 60-degree V12 mounted amidships, with two massive turbochargers fed by a big NACA duct on the roof. Excellent.

It develops 500bhp and 738lb ft of torque, which is 86bhp and 421lb ft more than the standard V8 petrol R8. Decent. The engine, lifted straight from the V12 TDI Touareg, is an exceptional one. But this is a supercar, and it's a diesel. How must it sound?

Thomas punches the starter button, mounted Ferrari mannetino-like on the steering wheel, and there is a brief whirr and then a zimmy sound. Don't know how to describe it other than 'zimmy sound', like a giant, extremely powerful sewing machine.

It's coming from behind our heads, and though it's by no means as intrusive as most mid-engined supercars, you're in no doubt that something significant is lurking back there.

The zimmy sound is accompanied by heavy breathing from the induction system, a compressed, hollow whoosh. And in the dim distance, like a far-away moan of some giant owl, is a deeper whine, very subtle but unmistakably a big-engine note.

Thomas's take on it is just as surreal as mine: "It's like 12 dwarves working, the cylinders, though they are not so small these dwarves." They certainly aren't. There isn't a hint of 'dieselness' or clatter, other than a very faint stuttering rhythm to the note at higher revs.

Thomas gives it no revs as we roll away on our brief journey down a quiet road near the harbour in Miami. Then he gives it more revs when he gets into third. Engine noise builds, but it's still a high-pitched mechanical zim dominating, along with a monstrous pipe-hitting breathing from the turbos.

The turbo whoosh dominates everything when you start to move along at pace. It's all turbo, this engine. It's a massive hollow pipe rush, like hearing white noise played at full blast down a two-foot-wide metal pipe.