The absolute threshold for two‐component tone bursts of 500‐msec and 1‐sec duration was measured as a function of the frequency spacing between the components. The average frequency of the two components was 700 Hz. When interpreted in terms of an energy‐detector model (peripheral filter followed by squarer, integrator, and threshold detector), the measurements give an estimate of the time constant and window shape of the integrator. Our measurements on two subjects give a time constant on the order of 200 msec. A window which initially decreases more rapidly than exponentially fits the data better than an exponential window.