Natural environments typically contain multiple sound sources. The sounds from these sources frequently overlap in time and often mask each other. Masking could potentially distort the representation of a sound's spectrum, altering its timbre and impairing object recognition. Here, we report that the auditory system partially corrects for the effects of masking in such situations, by using the audible, unmasked portions of an object's spectrum to fill in the inaudible portions. This spectral completion mechanism may help to achieve perceptual constancy and thus aid object recognition in complex auditory scenes.