Interaural Time Difference (ITD)

If your right ear is closer to a loudspeaker than your left ear, the result is that the sounds generated by the loudspeaker will arrive at your right ear before they arrive at your left ear. This difference in arrival times is termed an Interaural Time Difference or ITD. In the real world, ITDs are never very large: sound travels at about 340 meters per second, and so takes, at most, about 700-millionths of a second to cross to the other side of the head. Interestingly enough, the auditory system can easily measure such ITDs and uses them to help calculate the direction of a sound source. Under optimal conditions, listeners can detect ITDs as small as 10-millionths of a second.