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Audio Technology
How do AuSIM's products differ from generic "3D audio" products? Most products targeted at 3D Audio are designed to give game-quality performance, and are primarily used for computer games. AuSIM's products are designed for mission-critical applications and offer substantially higher standards of performance, both in terms of audio quality and perceived location accuracy. This includes customized physical modeling of sound propagation environments in software and higher speed and higher capacity hardware.
What is physical modeling and how is it used to generate 3D audio? Physical modeling is a method of synthesizing a real sound by using the physical characteristics of the sound source (whether it be a voice, an instrument, a machine, etc.), its propagation environment (such as air, water, etc.), and the listener. The physical characteristics important to 3D audio include location of the source and listener, shape, orientation and distance between the listener's ears, and sound absorptive / reflective / transmissive properties of the space. When the most important of the physical factors that affect the sound between the source and the listener are accounted for, a signal passed through the model will appear to be originating from a particular point in space.
What technology is AuSIM3Dtm built upon? AuSIM3D® is based on a dozen years of development by top scientists, theorists and engineers in the field of audio simulation. Early technology used DSPs to achieve needed levels of operation, but current general-purpose processors have made it possible to achieve acceptable performance without the expense and programming difficulties of DSPs.
What is tracking? Think GPS (Global Positioning Satellite) and then some. Tracking instruments deliver the relative location of an object to a reference point. There are 6 possible degrees of freedom of movement that can be tracked. The obvious degrees of freedom, X, Y, and Z, can be tracked with technology like GPS. The orientation that your head faces at that x, y, z location is measured in yaw, pitch, and roll – the last 3 degrees of freedom. Devices using electro-magnetic, ultrasonic, inertial, and optical technology are available that can track orientation.
Why is tracking so important to AuSIM3D®? In general, the ability of a person to localize sound is tremendously improved when they can move their head and listen to the relative perceived position of a sound from more than one orientation. The brain then uses these multiple references to interpolate a much more precise location of the sound. By incorporating head tracking into AuSIM3D®, the overall effect of 3D audio and the general localization precision is much greater.
Doesn’t hearing perception vary from person to person? Absolutely! Studies in the science of aural perception have identified specific characteristics that help define these person-to-person differences. A standardized set of tests can capture a particular head’s characteristics in a Head Related Transfer Function (HRTF). This function defines how a particular individual’s torso, upper body, head, and outer ear “shape” (or filter) sound as it travels from the surrounding air into the ear canal, and is generically referred to as “shape” or “shaping.” The HTRF can be used to “filter” 3D audio to match the individual’s characteristic.
Must I have my ears measured to use AuSIM3D®? No. Humans have the ability to learn or adjust to hearing with someone else’s ears. While “shaping” is unique to that particular individual, other people can interpret similar directionality and localization of sound from someone else’s HTRF filter. This directionality and localization is never as accurate as when hearing with the proper filter. When we add or remove headphones that “display” 3D audio with someone else’s ears, the brain immediately starts retraining to hear properly. The retraining process takes an indeterminate amount of time going in either direction, during which time 3D perception is not optimal.
Then what are the advantages of hearing measurement? In mission-critical applications where an operator must hear and localize a sound precisely and immediately, it is very important that the operator hear with their “own“ ears, or HTRF filter. This helps to remove any possible confusions, inaccuracies, or reversals (such as front to back) in the 3D audio perceived by a listener, as well as eliminating the additional inaccuracy during the retraining process.

Operators can have their personal physical characteristics captured in a custom HRTF filter sets. These can be precisely measured with AuSIM’s HeadZaptm system.
Will AuSIM3D® work in a CAVE? Yes, the technology has been designed specifically for interactive applications such as caves or other immersive environments. With the ability to integrate head-tracking devices and deliver a dynamic perspective of the aural world, alleviating the problem known as the “frozen perspective,” AuSIM3D® technology enables correct correlation of all moving graphics even with a moving subject.
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