The interaural level difference is the difference in loudness and frequency distribution between the two ears. As sound travels, its strength dissipates. For example, if you are very close to a loud sound, it will sound loud to you. But if you are some distance from the same loud sound, it will not be as loud. Think of a dog barking. If it is right in front of you, it will sound loud, but if the same dog barks across a big grassy field, the sound will be much less loud to you. Amazingly, our ears can detect loudness differences between the left and right ears. However, more important for sound localization is that the head casts an acoustic shadow, which changes the loudness and frequency distribution of sound going to each ear. We can define the acoustic shadow as the area on the side of the head opposite from the source of a sound in which the loudness of a sound is less because of blocked sound waves. The acoustic shadow is much more prominent for high-frequency sounds than it is for low-frequency sounds.
In this illustration, you can manipulate the different features of a tone to see how interaural level differences contribute to our perception of auditory direction.
To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.
Below is a list of the ways that you can alter the illustration. The settings include the following:
Play: will play to tone with the current settings listed below.
Play Series: will play a series of tones that will systematically vary the delay between the two ears.
Delay: change the delay begtween when the tone will be delivered to each ear.
Frequency (Hz): change the frequency of the tone.
Duration (ms): the duration of the tone in milleseconds.
Level Difference: select to use the interaural level differenc cue.
Time Difference: select to use the interaural time difference cue.
Pressing this button restores the settings to their default values.