As a result of the intended miniaturization of digital hearing aids, a quartz crystal cannot be used for generating the system clock. The inaccuracy of the system clock resulting therefrom cannot be tolerated in certain filter applications. It is thus proposed to adhere more precisely to the target value of the clock frequency of the system clock emitted by a clock generator by means of an externally generated clock signal. The external clock signal which can be generated for example in a remote controller for the hearing aid and can be transmitted wirelessly to the hearing aid is used to examine and if necessary readjust the system clock of the hearing aid. In this way, a relatively more precise and stable system c lock can be adhered to at least across more lengthy time segments and without the use of a quartz crystal in the hearing aid.