Institute for Telecommunication Sciences / Research Topics / Audio Quality Research / Public Safety Audio Quality / MRT Library

MRT Library

Project Description

Image shows engineer affixing SCBA mask.
An SCBA mask is affixed to a HATS in a sound chamber. We can configure the HATS to talk or listen. We use the HATS to produce audio files that are output through the mask, as well as files output without passing through the mask.

The PSCR program provided MRT audio files for researchers and developers in the fields of speech intelligibility testing. These are files we created to conduct our own speech intelligibility experiments. We are sharing these files with the public to support others researching speech intelligibility for public safety or other applications.

You can use the MRT audio files provided here with the ITS-developed software tool for objective estimation of speech intelligibility (technical paper here). The software tool, called ABC-MRT (available here), reduces the time and expense usually associated with MRT experiments to gauge speech intelligibility.

About the Audio Files

Our MRT files provide a digital audio library offering high-quality, royalty-free test material for R&D only. PSCR provides relevant audio files for different types of audio processing and quality measurement applications.

This library presents our audio material in two main sets:

  • Audio Source Files — Clean, high-quality, talker audio files and background noise audio files that we used, and you can use, as building blocks to create audio for R&D purposes.

  • Test Audio and Results Files — Audio created from the source audio files used in three experiments, along with the listener results data collected for each test.


The valuable assets provided here would not have been available without the many years of dedicated public safety audio quality research efforts of the late D.J. Atkinson. We thank ITS audio researchers Andrew Catellier and Stephen Voran for their meticulous work in curating this material.

DVSI is the owner and developer of the AMBE+2™ vocoder used in the APCO Project 25 radio standard, and provided the software used in the MRT experiments conducted by PSCR.

Additionally, we recognize Alan Wilson who developed the model for the analog radios used in the MRT tests after 2009 to comply with the analog specifications for bandwidth, deviation, frequency response, and sensitivity in the TIA-603 standard. The purpose was to permit a laboratory to control the signal-to-noise ratio for the analog radio model for long duration audio test conditions. Mr. Wilson also contributed files for bit errors and log-likelihood ratios for digital radio tests with vocoders using the modulation given in the TIA-102.BAAA and TIA-102.BBAB standards. This permitted comparable test conditions for analog and digital modes in radios of interest.


Certain commercial products, organizations, and companies are identified in this audio library material to specify adequately the technical aspects of the available audio files. In no case does such identification imply recommendation or endorsement by PSCR, NIST/CTL, or NTIA/ITS, nor does it imply that the products, organizations, or companies identified are necessarily the best available for the particular application or use.