Aircraft noise has been traditionally measured with either a few ground-based microphones or a linear ground-plane array of microphones. These techniques capture one-dimensional and/or two-dimensional characteristics of aircraft flight noise. The US Air Force Research Laboratory has started the construction of a 3-dimensional measurement facility at White Sands Missile Range in New Mexico. This facility, the Aeroacoustic Research Complex (ARC), will allow aircraft to fly through the array, collecting fully 3D acoustic data. ARC is initially being developed in two phases The first phase includes two 91.4 m tall towers separated by 244 m and will focus on noise from rotary wing and UAV aircraft. The second phase will add two 366 m tall towers separated by 610 m and will focus on large and high performance fixed wing aircraft. This facility will allow more accurate characterization of in-flight noise directivity by providing synchronized 3-dimensional magnitude & spectral acoustical signatures from 50+ microphones. ARC responds to a critical need for validation of existing predictive acoustic models. Such models are used for aircraft design, survivability, nonlinear acoustic propagation research and assessing noise exposure to residents living adjacent to airfields.
Although many psychoacoustic studies have been conducted to examine the detection of masked target sounds, the vast majority of these studies have been conducted in carefully controlled laboratory listening environments, and their results may not apply to the detection of real-world sounds in the presence of naturalistic ambient sound fields. Those studies that have examined the detection of realistic naturally-occurring sounds have been conducted in uncontrolled listening environments (i.e., outdoor listening tests) where the experimenters were unable to precisely control, or even measure, the specific characteristics of the target and masker at the time of the detection judgment. This study represents an attempt to bridge the gap between unrealistic laboratory listening studies and uncontrolled outdoor listening studies through the use of pseudorandomly-presented real world recordings of target and masking sounds. Subjects were asked to detect helicopter signals in the context of an ongoing ambient recording in a two interval detection task. The results show that the signal-to-noise ratio required to detect an aircraft sound varies across different types of ambient environments (i.e., rural, suburban, or urban).
Traditional auditory perceptual models for detection of complex signals against complex ambient soundscapes are based on the human audibility threshold imposed upon computed representations of auditory critical band filters. Such models attempt to locate a positive signal-to-noise ratio in any critical band and then apply classic signal detection theory to derive detectability measures (d′) and probability of detection values for the event. One limitation to these models is the limited experimental validation against human sound jury performance, especially using very low-frequency target signals such as helicopters. This study compares computational auditory detection model predictions against a corresponding large sample of human sound jury data points obtained in the laboratory. Helicopter and ambient soundscape signals were obtained from high-sensitivity recordings in the field. Playback in the laboratory was achieved under high-fidelity headphones calibrated to accommodate helicopter primary rotor frequencies with minimal distortion above human sensation level. All listeners completed at least 12 000 trials detecting helicopters against rural and urban soundscapes to represent the spectrum of potential environments involved in a real world scenario. Analysis compares the human sound jury performance against a contemporary computational auditory detection model, called “AUDIB,” developed by the U.S. Army and NASA.
Using Government drawings, specifications, or other data included in this document for any purpose other than Government procurement does not in any way obligate the U.S. Government. The fact that the Government formulated or supplied the drawings, specifications, or other data does not license the holder or any other person or corporation; or convey any rights or permission to manufacture, use, or sell any patented invention that may relate to them. This report was cleared for public release by the 88 th Air Base Wing Public Affairs Office and is available to the general public, including foreign nationals. Qualified requestors may obtain copies of this report from the Defense Technical Information Center (DTIC) (http://www.dtic.mil).
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