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The following paper contains a quantitative analysis of the effect of impulse noise on ideal frequency-modulation receivers. It is shown that two types of detected noise may result from an impulse transient. The amplitude and wave form of the generated noise are substantially independent of the amplitude or wave form of the initiating noise provided the noise transient exceeds the desired signal. Of the two types, the weaker is determined largely by the characteristics of the audio amplifier and results from a perturbation of the phase of the detector signal by the noise. The characteristics of the second and more objectionable type are established by the de-emphasis circuit and result when the phase of the detector signal is caused to slip one revolution by the noise. The question as to which type of noise will obtain is shown to be purely a matter of chance. An operational formula for the ideal detection process is also given from which both steady-state and transient solutions of the process of detection may be derived.