Abstract: A system for detecting and recording disturbances, e.g., transients, in periodic signals, wherein the system has a delay memory for storing sampled digital signal values of the periodic signals, is disclosed. In order to reduce the amount of data needed to be recorded, the sampled digital values are interim-stored in a read/write memory, from which the samples are read out each period of the periodic signal via an address control. The interim stored digital samples, which are the samples for the period of the periodic signal existing in time immediately preceding the present period, along with the samples from the present period, are fed to a digital comparator. The digital comparator compares the samples for the two signal periods, and depending on whether the samples differ by a predetermined threshold, generates a start or stop signal to an output device coupled to the delay memory for recording the occurrence of the disturbance.