A signal sampling circuit receives a clock signal indicative of a sampling rate and a periodic input signal to produce a digitized sampled output signal. The sampled signal is applied to an all-pass filter having a single pole/zero pair in which the pole/zero values are determined by a number supplied by a number generator. The number generator varies the applied number in a random or pseudorandom fashion to create a correspondingly random or pseudorandom variation of the transfer function of the filter. The filtered sample signal is then further processed by an absolute value operator and an average value operator for application to an amplitude responsive device such as a meter. The random or pseudorandom variation of the filter transfer function introduces a corresponding random or pseudorandom variation of the phase shift imposed upon the sampled signal within the filter. This. phase shift operates to impede or preclude the generation of erroneous beat note amplitude variations within the sampled signal for input signals having frequencies at or near the sampling rate or submultiples thereof.