u00d7 f s or 4 u00d7 f s it is pointed out that the intermediate signal o m still contains the interesting signal components above the final nyquist frequency of the analog to digital converter 2 but also contains some parts of the noise shaped quantization noise as well as signal components below the final nyquist frequency in the following example the intermediate sampling rate f m of the intermediate signal o m is 4 u00d7 f s i e the intermediate sampling rate f m is four times the final sampling rate f s it is expressly pointed out that the inventive idea is also applicable for intermediate signals o m having another intermediate sampling rate f m as for example 2 u00d7 f s or 8 u00d7 f s although the above mentioned examples are all integer multiples of the final sampling rate f s any real numbered multiples of the final sampling rate f s are implementable without departing from the concept of the present invention as an example and for reasons of simplicity the final sampling rate f s is assumed to be equal to 20 khz although the inventive idea is also applicable for similar sampling rates as the power consumption of the signal processing unit 3 is to be kept.