I'd like to pay attention to an application "Interaural Time Delay" by Samir Khan. His applications are interesting, based on real data, and mathematically accurate. Here is its introduction:
"Humans locate the origin of a sound with several cues. One technique employs the small difference in the time taken for the sound to reach either ear; this is known as the interaural time delay (ITD). This application modifies a single-channel audio file so that the sound appears to originate at an angle from the observer. It does this by introducing an extra channel of sound. Despite both channels having the same amplitude, the sound appears to come from an angle simply by delaying one channel".