CMI-8738 Datasheet, PDF (21/28 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
C3D HRTF Positional Audio Technology
C3D technology uses an audio filter called Head Related Transfer Functions (HRTFs), which
is licensed from CRL®(Central Research Lab). The basic concept of C3D is: since we can
hear sound three dimensionally in the real world using our two ears, it must be possible to
regenerate the same sound effect from two loud speakers.
What is HRTF ?
HRTF (Head Related Transfer Functions) is a set of audio filters which can vary locations of
sound effects (spatial hearing cues) in three-dimension measured from the listener's
eardrum.
People can use this technology and special digital signal processing to re-create spatial
hearing cues, so as to makes the ears hear a realistic and three-dimensional sounds coming
from a pairs of loud speakers or headphones.
There are several listening cues which allow people to hear
sounds three-dimensionally :
(I). Spatial Hearing : Primary 3D-cues
1. IAD
The head shadowing effect creates differences in the amplitudes of the sound signals
arriving at each ear from the source. The effects of diffraction are most noticeable in
the range between about 700 Hz to 8 KHz, where the A and S functions periodically
converge and diverge gently. This Inter-aural Amplitude difference (IAD) is one of the
primary 3D sound cues.
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