Air Force

Improved head-related transfer functions (HRTFs)

Rapidly and intuitively conveying accurate information about the location of a simulated sound source to a listener over headphones

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HRTFs are digital audio filters that reproduce the direction-dependent changes that occur in the auditory signals reaching the left and right ears when the location of the sound source changes.

Since the 1970s, audio researchers have known that the apparent location of a simulated sound can be manipulated by applying HRTFs to the sound before its presentation to the listener over headphones.

In effect, the HRTF processing technique works by reproducing the interaural differences in time and intensity that listeners use to determine the left-right positions of sound sources and the spectral shaping cues that listeners use for determining the up-down and front-back locations of sounds in the free field.

HRTFs can be a valuable tool for adding realistic spatial attributes to arbitrary sounds presented over stereo headphones. However, in the past, HRTF-based virtual audio displays have rarely been able to reach the same level of localization accuracy that would be expected for listeners hearing real sound sources in the free field.

To better simulate sound location, Air Force researchers have developed a novel HRTF enhancement technique that systematically increases the salience of the direction-dependent spectral cues that listeners use to determine the elevations of sound sources. The HRTF filters produce virtual sound sources over stereo headphones with more robust elevation localization performance than can be achieved with the current state-of-the-art in HRTF-based virtual audio display systems.

This spectral enhancement algorithm for the HRTF is flexible and generalizable. It allows an increase in spectral contrast to be provided to all HRTF locations within a cone-of-confusion rather than for a single set of pre-identified confusable locations. This results in a substantial improvement in spectral cues associated with auditory localization in the up-down and front-back dimensions and can improve localization accuracy, not only for virtual sounds rendered with individualized HRTFs but for virtual sounds rendered with non-individualized HRTFs as well.

Users of this technology may be aircraft pilots, unmanned aerial vehicle pilots, virtual reality players, scuba divers, parachutists, and astronauts. Or, more generally, applications may include any environment where a person’s orientation to the environment can become confused and quick reorientation is essential.

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

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