Stored waveform records representative of respective repetitions of a repetitive signal are processed by reading a first waveform record from memory to form a reference signal. A second waveform record is read from memory to form a second signal, and the second signal is shifted in time in such a manner as to minimize the power of a difference signal, of which the instantaneous magnitude is representative of the difference in instantaneous magnitude between the reference signal and the time-shifted second signal. If the waveform records are identical but for jitter, and the power of the difference signal is brought to zero, this implies that the first waveform signal is synchronous with the processed second waveform signal, i.e., there is no jitter between the two signals. If waveform records resulting from the reference signal and the processed second signal are then averaged, the level of noise in the averaged record is reduced relative to the stored records and the averaged record is free of distortion due to jitter.