A signal post-processing method is described, wherein a time-and-value-discrete signal is read from a memory by a signal post-processing circuit wherein a resolution bandwidth and a frequency range of the time-and-value-discrete signal are predetermined. A window filter is applied to the time-and-value-discrete signal. The window filtered time-and-value-discrete signal is transformed to a full-bandwidth frequency-domain signal. A sub-band is selected from the full-bandwidth frequency-domain signal by a selection unit wherein the rest is discarded by the selection unit. Further, a signal post-processing circuit as well as an oscilloscope are described.