David J. Atkinson; Stephen D. Voran; Andrew A. Catellier


This report describes speech intelligibility testing conducted on the Adaptive Multi-Rate (AMR) speech coder in several different environments simulating emergency response conditions and especially fireground conditions. The intelligibility testing protocol was the Modified Rhyme Test (MRT). Conditions included background noises of various types, as well as a mask associated with a self-contained breathing apparatus. Analog FM radio transmission and Project 25 digital radio transmission were also included in the test as reference points. Test participants were persons employed as first responders in public safety fields. Through statistical analysis of 26,900 MRT trials we are able to draw conclusions on speech intelligibility for AMR speech coding relative to analog and digital radio reference points for five different operating environments.

Corrected and re-issued March 2013.

Keywords: Project 25 (P25); subjective testing; analog FM; LMR; modified rhyme test (MRT); public safety; speech intelligibility; AMBE; AMR; fireground; MBE; SCBA mask; speech coder

For technical information concerning this report, contact:

Stephen D. Voran
Institute for Telecommunication Sciences
(303) 497-3839

To request a reprint of this report, contact:

Lilli Segre, Publications Officer
Institute for Telecommunication Sciences
(303) 497-3572

Disclaimer: Certain commercial equipment, components, and software may be identified in this report to specify adequately the technical aspects of the reported results. In no case does such identification imply recommendation or endorsement by the National Telecommunications and Information Administration, nor does it imply that the equipment or software identified is necessarily the best available for the particular application or uses.

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