Head-related transfer function
A head-related transfer function (HRTF) is a response that characterizes how an ear receives a sound from a point in space. As sound strikes the listener, the size and shape of the head, ears, ear canal, density of the head, size and shape of nasal and oral cavities, all transform the sound and affect how it is perceived, boosting some frequencies and attenuating others. Generally speaking, the HRTF boosts frequencies from 2–5 kHz with a primary resonance of +17 dB at 2,700 Hz. But the response curve is more complex than a single bump, affects a broad frequency spectrum, and varies significantly from person to person.
A sample of frequency response of ears: green curve: left ear XL(f) blue curve: right ear XR(f) for a sound source from upward front.
Sound localization is a listener's ability to identify the location or origin of a detected sound in direction and distance.
Interaural time difference (ITD) between left ear (top) and right ear (bottom). [sound source: 100 ms white noise from right]
Interaural level difference (ILD) between left ear (left) and right ear (right). [sound source: a sweep from right]