Page "Head-related transfer function" Paragraph 3

Humans estimate the location of a source by taking cues derived from one ear ( monaural cues ), and by comparing cues received at both ears ( difference cues or binaural cues ).

Among the difference cues are time differences of arrival and intensity differences.

The monaural cues come from the interaction between the sound source and the human anatomy, in which the original source sound is modified before it enters the ear canal for processing by the auditory system.

These modifications encode the source location, and may be captured via an impulse response which relates the source location and the ear location.

This impulse response is termed the head-related impulse response ( HRIR ).

Convolution of an arbitrary source sound with the HRIR converts the sound to that which would have been heard by the listener if it had been played at the source location, with the listener's ear at the receiver location.

HRIRs have been used to produce virtual surround sound.