What the heck are HRTFs?
They provide the brain with changing spectral characteristics or frequency response depending on the direction of particular sounds. The ridges of the pinna, as well as the other features of the head and shoulders act as multiple frequency-selective band-pass filters tuned to the azimuth and elevation of every sound in our environment. The minute shifts in frequency response, phase and sound level gives the brain the data to localize the sounds. Without HRTFs our ancestors would have been all eaten up by predators and we might not be here today! You can test this phenomenon easily by snapping your fingers, first directly in front of you and then at the same distance to your right or left. Notice the entirely different timbre of the sounds — duller when in front and with more high frequencies when to the side where the sound is directed on a straight path right into your ear canal. You can also have someone snap their fingers behind you as well as in front while your eyes are closed. T
