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PSCR Releases Audio Files for Intelligibility Testing

May 31, 2013 by

NTIA’s Institute for Telecommunication Sciences (ITS) in Boulder, CO, has been hard at work for years on research aimed at giving first responders next-generation technology that will help save lives.

The public safety research is done through a joint venture between ITS and the National Institute of Standards and Technology (NIST) Law Enforcement Standards Office (OLES), called the Public Safety Communications Research Program (PSCR).  PSCR is hosting a Stakeholder Conference in Westminster, Colo. June 4-6 to bring together representatives from public safety, Federal agencies, industry, and academia to learn about PSCR’s recent work efforts related to the build out of the First Responder Network Authority (FirstNet) nationwide public safety broadband network.

Beyond the research PSCR is doing for FirstNet, a key area of research at PSCR over the years has been improving the quality of voice communications on digital radios used by public safety.  PSCR recently released audio files used as part of a series of tests focused on enhancing the sound quality of digital radios used by public safety officials. The audio files will be a valuable resource for other researchers, and are now on the PSCR web site: .

Public safety practitioners rely heavily on wireless voice communications when responding to an emergency. Voice communications remain the bedrock tool for managing incident responses and for day-to-day activities. Above all, public safety communication devices must be able to deliver intelligible speech in any number of very challenging noise environments. But when the new digital systems were introduced, first responders began having difficulties understanding voice transmissions when working in very noisy situations. While legacy analog systems remained intelligible, they required more bandwidth to operate.

To address this critical safety-of-life issue,  ITS began at the beginning of the last decade to develop test plans to measure the intelligibility of digital land mobile radio (LMR) communication systems when used in high-background noise environments experienced by firefighters. This important work paved the way for changes in technology and best practices that led to the introduction of digital radios with improved speech intelligibility.

In digital radio systems, speech intelligibility depends to a great extent on the ability of the digital voice coder (or “vocoder”) to distinguish between speech and background noise. PSCR conducted a series of three tests between 2008 and 2012 with public safety practitioners. Information from these tests helped shape improvements in vocoder programming, product design, and best practices recommendations that enhanced intelligibility. The most recent tests (see the NTIA blog provided important information relevant to vocoders proposed for emerging public safety broadband communications systems.

The audio test files used to conduct the tests were “processed” by mixing clean, high-quality, talker-only recordings with background noise and then passing the result through various public safety communication systems. The intelligibility tests used a process called the Modified Rhyme Test, recommended by the National Fire Protection Association (NFPA) and the American National Standards Institute (ANSI), to test intelligibility. In an MRT trial, a subject must identify the word heard from a set of six words that rhyme. The MRT Library created by ITS contains more than 20 GB of data, including the 150,000 processed recordings used during the three reported tests. The original high-quality clean recordings from a variety of male and female talkers are also posted, as are high-quality background noise loops. Industry and academic researchers can use these clean files to create mixed recordings for other types of tests. All the audio clips are freely available, but researchers must agree to use the files solely for internal research and development purposes to test audio processing methods and assess audio quality.

The MRT Library complements the public safety offerings of the Consumer Digital Video Library (CDVL), hosted by ITS and overseen by a technical committee that includes representatives of industry and academia. The CDVL makes high quality, uncompressed video clips freely available for research into assessing the quality of video that has been compressed for efficient wireless transmission. The CDVL collection was originally developed to support quality testing of different ways of compressing entertainment video streams for broadcast. Recently, the collection has been expanded to include clips that can be used for research related to the functional video requirements of public safety practitioners, such as video clips that show EMS calls. These video clips make possible research into compression mechanisms that deliver video of sufficient quality to be used for emergency telemedicine, for example.

PSCR is a collaborative inter-agency project sponsored by the Department of Homeland Security (DHS) Office for Interoperability and Compatibility (OIC), the DHS Office of Emergency Communications (OEC) and FirstNet.  PSCR laboratories located within ITS provide research, development, testing, and evaluation to foster nationwide communications interoperability. Through active engagement of public safety practitioners in this research, PSCR provides contributions to wireline and wireless standards committees developing standards for voice, data, image, and video communications to ensure that the critical requirements of public safety are supported by emerging standards.