The auditory stimuli were continuous 3D binaural sounds synthesized with nonindividualized HRTFs from the Massachusetts Institute of Technology (MIT) dataset (Gardner & Martin, 2000), auditory icons (sounds that create an analogy with real-world events and situations), and "earcons" (abstract, symbolic sounds used to facilitate the players' navigation through the complex content of the game) (Csapo and Wersenyi, 2013).
Because they were modifying their position in respect to the active target and the surrounding obstacles, they could perceive changes in both the spectral content of the sound, its intensity, and its localization simulated with HRTFs.
It is also possible that the discrepancy between performance in the free-field condition and performance in the virtual condition was attributable to the use of nonindividualized HRTFs
in the generation of the virtual cues.
HRTF measurements stopped and an auditory feedback signal was given when the deviation along the x, y, or z coordinate exceeded 0.
After completion of the free-field HRTF measurements, Sennheiser HD 530 headphones were placed over each participant's ears, and the transfer function from headphone to ear canal was determined for both ears.
When you listen through speakers, your outer ears are part of the listening process and so only partial HRTFs
are required in the signal-processing", explained Dr.
Additionally, Oak's support for HRTF
enables 3D positional multi-channel sound.
When combined with Microsoft's DirectSound standard, this architecture provides multiple audio channels that can be used for music reproduction, audio special effects and positional HRTF 3D sound.
According to Barrie Davis, Managing Director of Xitel, "We have chosen Oak's OTI-610 as the digital controller component of the XA20 PCI sound card because of its audio software support for not only Aureal's A3D HRTF sound algorithms but also for Microsoft's DirectSound 5 multiple digital audio channels and HSP Wave Table synthesis.
The main disadvantages of nonindividualized HRTFs
are increased frequency of front/back reversals and more difficulty in simulating elevation (Wightman & Kistler, 1989).
This encoding is accomplished by digitally filtering a sound source by means of a FIR (finite impulse response) filter created from measurements of HRTFs
, which represent the direction-dependent modification of a sound source by the person's head, torso, and pinnae (see Wightman and Kistler, 1997, for a review).