The driver's and passenger's belt have three microphones, each smaller and flatter than shirt buttons, so that they don't interfere with the seatbelt mechanism.
Quality signal whatever the user's height
Audi says that when the seatbelt is worn one microphone is always located in the vicinity of the person's mouth, regardless of their height, so it gives the best possible speech reproduction even with the roof down.
Software analyses the quality of the signals from the mikes and forwards the best signal to the hands-free unit.
A fourth microphone, mounted on the windscreen frame, is used to make calls when the car is parked and the seatbelt is not on.
We've driven the R8 Spyder and our first impressions of the technology are good. What Car? road test editor Peter Tullin said: 'It's a very neat trick and it seems to work very well.'