The duplex theory states that ITDs are used to localise low frequency sounds, in particular, while ILDs are used in the localisation of high frequency sound inputs. However, the frequency ranges for which the auditory system can use ITDs and ILDs significantly overlap, and most natural sounds will have both high and low frequency components, so that the auditory system will in most cases have to combine information from both ITDs and ILDs to judge the location of a sound source.