The masking produced by two, equal‐intensity sinusoids on a signal, a third sinusoid located midway in frequency between the two maskers, is measured as a function of the frequency separation between the two maskers. Three signal frequencies are used 250, 1000, and 4000 cps. At small frequency separations, the detectability of the signal is independent of center frequency and simply dependent on the frequency separation of the two maskers. As larger frequency separations are approached, the masking suddenly diminishes and this larger critical frequency separation, which is frequency‐dependent, is approximately the width of the envelope of excitation on the basilar membrane when excited by a sinusoid. The interpretation of these results in terms of a simple energy detector followed by a simple integrator is discussed.