Abstract: Apparatus for generating a single pulse the first time only that a noisy cyclic signal exceeds a reference level during a half-cycle. For the positive half of a cycle of the noisy cyclic signal, a comparator 12 and a multivibrator 14 produces a fixed voltage output when the noisy cyclic signal first exceeds the reference level. A multivibrator 23 stops the production of the fixed voltage output when the noisy cyclic signal next passes the zero voltage level in the negative direction. Consequently, a single pulse is generated indicating that the signal exceeded the reference level during that half-cycle. Comparator 16 and multivibrator 17 are for producing pulses whenever the noisy cyclic signal exceeds the reference level during the negative half-cycle.