The invention relates to a device and a method for switching currents in a stator winding of a generatorelectric motor combination, said stator winding comprising at least one winding which can be short-circuited or switched in a highly-resistive manner by means of at least one device. Information indicating the error in an engine unit is stored in a non-volatile memory, the engine unit based on the information stored in the non-volatile memory is power-distributed in a case where the image forming apparatus starts up, and if the error is detected in the engine unit that was power-distributed, notification of the error in the engine unit is made. The brushes are in mechanical cooperation with the wheels allowing the wheels and brushes to spin in substantially opposite directions. There is provided a method for generating spectral envelope estimates from a digitized utterance.