Interaural Time Delay and Spatial Location

This Applet demonstrates how interaural time delay (ITD) can make it seem like a sound is closer to one ear than another. There are a number of other sound features that help us locate a sound, including amplitude, reverberation, and head related filtering. But this Applet focusses on ITD.

To Do:

• Put on headphones and turn off your loudspeakers. This effect works best with headphones but can sometimes be heard on loudspeakers. Adjust the Amplitude to a comfortable level, not too loud.
• Move the ITD fader between -1.0 and +1.0. This controls the relative delay for the sound reaching each ear. Notice that the sound seems to move from one ear to the other. Note that if you go much beyond +/-1.0 that the effect does not increase. This is because the distance between your ears is about one foot, which corresponds to just over one millisecond of delay. The speed of sound is about 1125 feet per second. So a millisecond delay corresponds to 10.6 inches.
• Move the ITD fader to 1.0 and then listen to just the left and the right earpiece independantly. Notice that the sound is just as loud in each ear. This shows that we are not using stereo panning to achieve this effect.
• Increase the frequency and notice that the effect is diminished. This is because the wavelength of higher frequencies is less than the size of your head so it is harder to distinguish the phase difference.