Auditory parallax effects in the HRTF for nearby sources

When a sound source is close, the angle of the source relative to the center of the head can differ substantially from the angle of the source relative to the ear. Since the high-frequency features of the HRTF (head related transfer function) are known to depend on angle of the source relative to the ear, this "acoustic parallax" should produce a systematic remapping of high-frequency features in the far-field ipsilateral HRTF to more lateral locations in the near-field HRTF. HRTFs measured on an acoustic manikin indicate that this type of remapping does occur in the near field, and that the frequency response of the pinna is roughly independent of distance when the source is more than 5 cm from the ear. The perceptual relevance of the acoustic parallax effect is briefly discussed, along with its potential application to near-field virtual audio displays.