Air Force

Enhanced sound location

Much better auditory localization accuracy than existing virtual audio systems

Software & Information Technology

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FIG. 1 illustrates such a conventional cone of confusion 10 where all possible source locations that produce roughly the same ILD and ITD cues are positioned at an angle, β, from an interaural x-y-z axis 12. Within this cone 10, localization judgments have to be made solely on spectral cues generated by the direction-dependent filtering characteristics of the listener’s external ear. If spectral cues are not precisely reproduced by the virtual audio display system, then poor localization performance in elevation may result.

Virtual audio display systems allow listeners to make exploratory head movements while wearing removable headphones; however, it has historically been very difficult to achieve a level of localization performance that is comparable to free field listening. Listeners are generally able to determine lateral locations of virtual sounds because these left-right determinations are based on interaural time delays (ITD) and interaural level differences (ILD) that are relatively robust across a wide range of listening conditions. However, listeners generally have extreme difficulty distinguishing between virtual sound locations that lie within a so-called cone-of-confusion.

To deal with this issue of locating sounds on a vertical plane, Air Force scientists have developed a method of using a head related transfer function (HRTF) to enhance polar localization of an audio signal. The system determines a magnitude response for each channel of the audio signal. The magnitude response is decomposed to a polar-coordinate system and enhanced. The enhanced responses for each channel of the audio signal are then combined.

This novel spatial audio system (SAS) systematically increases the salience of the direction-dependent spectral cues that a listener uses to determine the elevations of a perceived sound source. In that regard, the SAS is configured to produce a sound over headphones that is perceived to originate from a specific spatial location relative to the listener’s head. The system includes an analog-to-digital converter that converts an arbitrary analog audio input signal into the discrete-time signal. The input signal is separated by a signal splicer into a left ear signal and a right ear signal. Left and right digital filters are each associated with look-up table filters with an enhanced HRTF to create digital signals for a particular virtual source.

Such systems and methods offer a capability that may be useful in an aircraft cockpit display where it might be desirable to produce a threat warning tone perceived to originate from the location of the threat relative to the pilot. Still other areas of use may include unmanned aerial vehicle pilots, SCUBA divers, parachutists, astronauts, or, generally, any environment wherein the orientation to the environment may become confused and quick reorientation may be essential.

This US patent 9,173,032 is closely related to US patent 8,428,269.

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