Under the Advanced Extravehicular Activity program, the NASA Glenn Research Center is responsible for Communications, Avionics, and Information subsystems for next-generation exploration space suits. As part of the communications subsystem, the audio signals to and from the space suit are critical to mission success, providing voice communications between astronauts and mission control, between astronauts, and potentially from astronauts to voice-commanded robots and computers.
The space suit environment presents a unique challenge for capturing and transmitting speech. Inside the space suit, high levels of reverberation, flow noise, and machine noise exist together with very short direct-propagation paths. Static pressure levels can range from a fraction of an atmosphere during actual extravehicular activity operations to strong hyperbaric conditions during terrestrial field testing. Because an astronaut is afforded a wide range of motion within the suit, the physical geometry between an astronautís mouth or ear and any particular fixed location on the inside of the suit varies significantly over time. In addition, problems were identified recently regarding the proper function of existing communications caps over wide ranges of pressure and regarding flow noise.
The resolution of technical issues surrounding speech audio capture and transmission systems--cap-based or otherwise--requires a testing facility that can support the development and evaluation of in-helmet audio solutions and that can provide a full complement of engineering data on the acoustic environment in a rigorous and repeatable fashion. The Space Audio Development and Evaluation Laboratory (SPADEL) at Glenn fills this requirement by providing the ability to measure in-helmet acoustic characteristics as well as the ability to evaluate the speech quality associated with in-helmet audio production and sensing devices.
The basic focus of SPADEL is to provide a means to assess the effects of the acoustic path on the speech communications channel to and from an astronaut. Current capabilities include traditional testing and evaluation methods that focus on engineering quantities such as frequency response and distortion levels. SPADEL also can evaluate speech in terms of listening quality and listening effort. Speech quality testing is accomplished primarily through the use of a computerized device that implements International Telecommunication Union (ITU)-recommended speech-quality algorithms.
In addition, SPADELís controlled acoustic environment, together with its sophisticated sound production and recording capabilities, can be used to develop reference recordings for subsequent jury testing that produces true Mean Opinion Score (MOS) assessments of speech quality. SPADELís computerized speech-quality testing device produces estimates of the MOS that have been shown to be highly correlated with the actual MOS created using jury testing, but with significantly less time and cost. Note that SPADELís speech-quality testing tool can evaluate other portions of the speech channel such as speech coding and packetizing. Thus, in addition to measuring the speech quality of the acoustic paths within a space suit, SPADEL can measure the intelligibility of almost any part of the speech communications channel. Speech quality testing can be extended to the complete, end-to-end speech channel.
A NASA engineer tests sound-pressure levels on an anthropomorphic mannequin inside a space shuttle hard upper torso and helmet.
Alan N. Downey, 216-433-3508, Alan.N.Downey@nasa.gov
Dr. O. Scott Sands, 216-433-2607, Obed.S.Sands@nasa.gov
Glenn R. Lindamood, 216-433-8582, Glenn.R.Lindamood@nasa.gov
Amy R. Asmus, 216-433-3703, Amy.R.Asmus@nasa.gov
David A. Carek, 216-433-8396, David.A.Carek@nasa.gov
Authors: Alan N. Downey and Dr. O. Scott Sands
Headquarters program office: Exploration Systems Mission Directorate
Programs/projects: Human System Research and Technology
Last updated: December 14, 2007
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