A method for operating an electric machine with a power source, an electric motor, and an intermediary power converter, in which an input current of the power source is converted to a multi-phase output current for the electric motor by a pulse width modulated control of a number of semiconductor switches of the converter, wherein the or each pulse is generated at a first point in time and terminated after a pulse duration at a second point in time, in which for each alternating current component, which is generated in the course of the pulse-width-modulated driving of the semiconductor switches in an intermediate circuit of the power source, a frequency spectrum is determined, and in which the pulse durations of the pulses of the pulse width modulated control can be set such that the sum of the frequency spectra of the alternating current components is minimal.