Audi is readying the most desirable RS5 yet – a stunning cabriolet version, which our spies have spotted testing near to the Nurburgring circuit in Germany ahead of its debut next year.With the same bulging wheelarches as the coupé model, it certainly stands out from the S5 Cabriolet – and it has even more performance. Under the bonnet, the RS5 Cabriolet will have the same 4.2-litre V8 engine as the coupé, which produces 444bhp and 430Nm of torque.This drives all four wheels through a quattro drivetrain and a seven-speed twin-clutch S tronic gearbox, and should take the car from 0-62mph in under five seconds and on to a limited top speed of 155mph.The RS5 Cabriolet will use the same triple-layered electrically operated folding canvas roof as the S5 drop-top, and that means it will be heavier than the coupé, as engineers will have to strengthen the chassis to cope with the loss of the hard-top.However, while performance will be ever so slightly down on the coupe, the RS5 Cabriolet will make up for this by putting drivers even closer to the sound of the mighty V8 engine.The new model will also adopt the latest RS5 coupé’s facelift. This will include new front and rear lights, a smoother and simpler bumper and a revised grille. The car will debut at March’s Geneva Motor Show, before going on sale in the UK in time for summer, priced around £60,000.Meanwhile, Audi is developing technology that could make lesser models sound like performance versions. Using lessons learned from the new S8, which features speakers fitted within the exhaust system itself, the firm is set to team them up with synthesisers to pipe rorty sounds into the cabin. The technology can be applied to regular cars and electric cars.