CMI-8738 Datasheet, PDF (23/28 Pages) C-Media Electronics – C3DX PCI-Based HRTF 3D Extension Positional Audio Chip

Ver. 1.2
CMI-8738/PCI-SX AUDIO Specification
HRTF 3D Positional Audio Technology White-Paper
3. Pinna Effects
It has been presumed by several researchers that the convolutions of the pinna create
the spectral features which constitute the 'height' cues. In practical experiments by
Gardner, in which different parts of the pinna were occluded, and then the ability of a
number of subjects to identify sound source positions at different heights was tested, it
was shown that the different features all contributed by different amounts. For example,
if the fossa is excluded, then height localization capability is impaired, but not totally
extinguished. It would be reasonable to conclude that it is the combined effect of the
pinna convolutions which create the various localization cues, and it is not valid - or
logical - to attempt to assign particular spatial capabilities with individual physical
features.
(II). Spatial Hearing : Secondary 3D-cues (shoulder & local reflections)
In addition to the 'primary' 3D sound cues (IAD, ITD and pinna effects), there are several
additional cues which do contribute to the localization capability; these will be referred to
here as 'secondary' cues, and include shoulder/torso reflections, local room reflections, and
psychological cues.
1. Shoulder / Torso reflections
The presence of a torso attached to an artificial head has the effect of increasing the
pressure in the vicinity of the ear up to frequencies of around 2 kHz. The effect is greater
for frontal sources than lateral ones. In experience, the presence of the torso does not
appear to contribute much to spatial accuracy. However, shoulders are located very close
to the ears, and their effect is greater, this time, in respect of
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