An audio processing device comprises a multitude of electric input signals, each electric input signal being provided in a digitized form, and a control unit receiving said digitized electric input signals and providing a resulting enhanced signal. The motors can be variably driven using pulse width modulation, with duty cycle compensation for voltage drops resulting from added loads and with current limiting when, for example, the system is powered from an AC line using a low voltage transformer of limited capacity. The rotor module is located in an electromagnetic field, and has a multipolar magnetic rotor and a rotating axle. In the blade holder, there is also a separate backing blade, which is fitted at one edge into the blade holder, the other edge extending closer than the blade holder to the said bevelled edge.