by John Schutte
Air Force Research Laboratory
Scientists at the Air Force Research Laboratory (AFRL) are working to improve general aviation safety with three-dimensional (3-D) sound cues that can help air traffic controllers monitor aircraft and help pilots fly straight and level.
Normally, humans hear sound from all around. The human auditory system can discern, to a certain degree, both the location of a sound and its distance from a listener.
In some situations, however—such as when pilots and air traffic controllers are wearing monaural communications headphones—lack of natural audio cues can cause confusing and potentially hazardous situations when multiple talkers "stack up" in a listener's head.
The basic concept of 3-D audio is to use stereo headphones to simulate spatially separated sounds when natural cues are not available. Aviation communications typically provide flat, one-dimensional sound with no indication of direction or distance. But with 3-D audio, a person wearing stereo headphones hears sounds as he would normally, coming from varying directions and distances.
AFRL's 3-D "audio display" is also dynamic; if a listener hears a sound from the right and turns his head toward the sound, the sound then appears to be in front of the listener.
In multi-talker situations, 3-D audio improves speech intelligibility by spatially separating the sources, thus helping a listener track and understand multiple simultaneous conversations, according to Douglas S. Brungart, Ph.D., technical advisor for AFRL's Human Effectiveness Directorate, Warfighter Interface Division, Battlespace Acoustics Branch.
"Any communications situation with more than one talker is a potential application,"
Brungart said. "That could be as simple as a two-person teleconference or as complicated as air traffic control systems where an operator has to listen to nine or ten radios at once."
With 3-D audio, air traffic controllers could more easily distinguish between radio
transmissions from multiple aircraft pilots, and tower controllers could keep track of the locations of aircraft taxiing to and from the runways of a busy airport.
This could increase their situational awareness and potentially help prevent accidents both on the ground and in the air. For pilots, AFRL researchers developed an artificial audio horizon to augment a pilot's visual horizon. In tests at NASA Langley Research Center, subject pilots wore opaque goggles for attitude recovery tests—literally flying blind, using only sound cues piped through the aircraft's communications system as a guide to recover from displaced orientations.
Sound—in this case the pilots' favorite music—is an artificial horizon to which pilots fly the aircraft. Software filters correlate the music with the aircraft's pitch and roll—for example, the sound moved left to indicate left-wing high—allowing pilots to determine the aircraft's attitude and make corrections.
AFRL partnered with commercial vendor Compunetix, Inc., to upgrade its commercial software and install it at the Nellis Air Force Base weapons test range in Nevada, where operators talk to multiple aircraft during training exercises.
Under a CRADA with Telephonics Corporation, AFRL demonstrated the feasibility of integrating 3-D audio into airborne secure digital intercommunication systems.
Other potential 3-D audio applications include providing sound cues to alert blind persons to the location of objects; improving situational awareness for foot soldiers in combat situations and firefighters in smoke-filled buildings; and integrating realistic audio into video/PC games and training simulators.
Wright State University and the Air Force Research Laboratory's Human Effectiveness Directorate are collaborating to transfer 3-D audio technology developed for fighter aircraft to general aviation cockpits. The technology will help pilots keep track of the locations of other aircraft, maintain course while engaged in other tasks, and avoid disorientation. As shown here, this project uses a flexible flight simulator that allows rapid and
economical integrations of new instrumentation concepts, and safe replication of dangerous or unusual flight situations.
The Auditory Localization Facility (ALF) at the Air Force Research Laboratory's Human Effectiveness Directorate enables research in binaural and spatial hearing, measurement of head-related transfer functions, and development of 3-D audio systems. ALF is a 4.26-meter-diameter geodesic sphere inside an anechoic chamber. The sphere contains 277 loudspeakers and can present 16 sounds simultaneously from selected or all locations,
simulating complex real-world auditory environments.
