The temporal constraints of auditory event synthesis were investigated using event-related potentials. Standard stimuli consisted of an initial constant-frequency segment followed by a frequency glide. Occasionally, stimuli deviating from this standard both in intensity and within the direction of the glide were presented in the otherwise repetitive sound sequence. Previous results suggested that such 'double' deviants elicit only a single mismatch negativity (MMN) if the two temporally separate deviant elements were integrated within a common unit. Two successive MMNs were elicited by double deviants when the initial constant-frequency segment of the sound was 250 ms long, but only one when this segment was 150 ms in duration. The results support the hypothesis that the auditory input is processed in approximately 200 ms long temporal integration windows.