A data processing system is disclosed including a data processor for operating on data samples received from a data source, a digital to analog converter arranged to receive the data samples from the data processor and to convert the received data samples into an analog signal, and a controller arranged to monitor the magnitude of the data samples received from the data source and disable one or both of the data processor means and the digital to analog converter when the magnitude of one or more received data samples falls within a predetermined magnitude range. Such a system is able to operate in a low-power mode that may be advantageous for battery-powered device or other applications where power conservation is important.