NASA has a long history of investigating human response to aircraft flyover noise and in recent years has developed a capability to fully auralize the noise of aircraft during their design. This capability is particularly useful for unconventional designs with noise signatures significantly different from the current fleet. To that end, a flexible software architecture has been developed to facilitate rapid integration of new simulation techniques for noise source synthesis and propagation, and to foster collaboration amongst researchers through a common releasable code base. The NASA Auralization Framework (NAF) is a skeletal framework written in C++ with basic functionalities and a plugin architecture that allows users to mix and match NAF capabilities with their own methods through the development and use of dynamically linked libraries. This paper presents the NAF software architecture and discusses several advanced auralization techniques that have been implemented as plugins to the framework.

An open architecture for auralization has been developed by NASA to support research aimed at understanding human response to sound within a complex and dynamic soundscape. The NASA Auralization Framework (NAF) supersedes an earlier auralization tool set developed for aircraft flyover noise auralization and serves as a basis for a future auralization plug-in for the NASA Aircraft Noise Prediction Program (ANOPP2). It is structured as a set of building blocks in the form of dynamic link libraries, so that other soundscapes, e.g., those involving ground transportation, wind turbines, etc., and other use cases, e.g., inverse problems, may easily be accommodated The NAF allows users to access auralization capabilities in several ways. The NAF's built-in functionality may be exercised utilizing either basic (e.g., console executable) or advanced (e.g., MATLAB, LabView, etc.) host environments. The NAF’s capabilities can also be extended by augmenting or replacing major activities through programming its open architecture. In this regard, it is envisioned that third parties will develop plug-in capabilities to augment those included in the NAF.

The Exterior Effects Room (EER), located at the NASA Langley Research Center, is a facility built for psychoacoustic studies of aircraft community noise. Recently, the EER was significantly upgraded to allow for simulation of aircraft flyovers in a 3-D audio and visual environment. The upgrade included installation of 27 satellite and 4 subwoofer loudspeakers that are driven by a real-time audio server. The audio server employs an implementation of the vector base amplitude panning method to position virtual sources at arbitrary azimuth and elevation angles in the EER. Real-time application of filters, time delays, and gains are required to compensate for installation effects, including those associated with the irregular room geometry, colorization due to varying loudspeaker installations, and crossover filtering. The authors previously showed [J. Acoust. Soc. Am., 127, 1969 (2010)] that color compensation and crossover filtering could be achieved for satellite and subwoofer loudspeakers. However, the resulting FIR filters were too long (32 768 taps) to implement in real-time. The focus of this work is on the development of reduced-length surrogate IIR filters and on the measurement of the acoustic performance of the installed real-time system.

The Exterior Effects Room (EER) at the NASA Langley Research Center is a 39-seat auditorium built for psychoacoustic studies of aircraft community noise. The original reproduction system employed monaural playback and hence lacked sound localization capability. In an effort to more closely recreate field test conditions, a significant upgrade was undertaken to allow simulation of a three-dimensional audio and visual environment. The 3D audio system consists of 27 mid and high frequency satellite speakers and 4 subwoofers, driven by a real-time audio server running an implementation of Vector Base Amplitude Panning. The audio server is part of a larger simulation system, which controls the audio and visual presentation of recorded and synthesized aircraft flyovers. The focus of this work is on the calibration of the 3D audio system, including gains used in the amplitude panning algorithm, speaker equalization, and absolute gain control. Because the speakers are installed in an irregularly shaped room, the speaker equalization includes time delay and gain compensation due to different mounting distances from the focal point, filtering for color compensation due to different installations (half space, corner, baffled/unbaffled), and cross-over filtering.

This report completes the project entitled “Concept and Technology Exploration for Transparent Hearing Systems”, funded by the US Air Force Research Laboratory at Wright-Patterson Air Force Base in collaboration with Natick Soldier Systems of the US Army. The document outlines the project as planned and details the project as executed. Given the importance and time criticality of determining a solution to the problem addressed, the project team exploited knowledge gained during the project, redirecting the plan as necessary to maximize exploration. This document outlines the goals of the project, provides an overview of previous relevant work, discusses the work planned for the project, details the work and its findings, and describes how a solution system could be integrated into a dismounted soldier’s personal information system.The intended audience for this document includes the project sponsors, the intermediate contract managers, designated reviewers, and future helmet system designers. Additionally, the report authors assume the document may be published to a wider audience. The designated reviewers may encompass professionals in the fields of hearing, signal processing, sensors, warfighting equipment, hearing enhancement/augmentation, and aural displays, who can give feedback and guidance to extensions of the project.

: Modern militaries are challenged to physically protect open-field personnel from a great variety of life and effectiveness threats, including chemical, biological, laser, ballistic, and percussive weapons. Many chemical and biological threats require covering all orifices, including the ears, to achieve minimal protection. Additionally, warfighting involves operating in very close proximity to loud equipment, from which the noise can degrade an individual 5 auditory perception, and over time can degrade general performance. Common hearing protection and occlusion isolates the warfighter from the environment, deflating situational awareness, confidence, and effectiveness, thus putting the warfighter at high risk and compromising his ability to detect and assess threats. Often, soldiers are so uncomfortable with the isolation of hearing protection that they will choose to go without hearing protection and expose themselves to painful and harmful noise, which can result in deafness and reduced effectiveness as warfighters. This effort includes a survey of relevant head-borne hear-through auditory systems, a selection of approaches to a transparent hearing solution, implementation of the approaches, and evaluation.