Most sampled signals are not simply stored and reconstructed. But the fidelity of a theoretical reconstruction is a customary measure of the effectiveness of sampling. That fidelity is reduced when "s"("t") contains frequency components whose periodicity is smaller than two samples; or equivalently the ratio of cycles to samples exceeds ½ (see Aliasing). The quantity ½ "cycles/sample" × fs "samples/sec" = fs/2 "cycles/sec" (hertz) is known as the Nyquist frequency of the sampler. Therefore, "s"("t") is usually the output of a low-pass filter, functionally known as an "anti-aliasing filter". Without an anti-aliasing filter, frequencies higher than the Nyquist frequency will influence the samples in a way that is misinterpreted by the interpolation process.