for a complete beginner's intro to the fascinating world of neuroscience.
acoustics & signal processing
The numbered squares signify the sound directions corresponding to a series of "virtual acoustic space" stimuli, which were generated by convolving a stimulus - in this case, a series of tapping sounds - with the head-related transfer function of one of the authors of this book.
Move the mouse cursor over the grid below to hear a harmonics complex tone with ILDs and ITDs as indicated.
You should listen to these sounds over headphones, and this demo may not work for you if you have a significant hearing loss in one ear, or if the sound card on your computer is of poor quality and does not separate the two stereo channels well.
As explained in the section on modes of vibration. most natural sound sources will not emit pure tones, but sounds composed of many, often harmonically related frequencies. Now, some texts on hearing will tell you that the pitch of a sound is "related to the sound's frequency", but if a sound contains many (possibly harmonically related) frequencies then it may not be at all obvious which of the sound's frequencies determines the pitch.
Chapter 3 of Auditory Neuroscience discusses the pitch intervals used western music in great detail. For convenience, a table of fundamental frequencies for equal-tempered scale is copied below from http://www.phy.mtu.edu/~suits/notefreqs.html
By convention A4 = 440 Hz
This page has little animations illustrating the two major binarual cues for sound source direction: Interaural Time Differences (ITDs) and Interaural Level Differences (ILDs).
In the "free field" (meaning in the absence of obstacles that might interfere with wave propagation), sound waves will spread out in all directions, like spheres radiating out from the source at the speed of sound.