December 2017 | NTIA Technical Report TR-18-529
Abstract: Frame erasures and background noise are two factors that can interact with speech coding to reduce speech intelligibility and thus impair public safety mission-critical voice communications. We conducted two tests of intelligibility in the face of these factors. The tests covered five adaptive multi-rate (AMR) and enhanced voice services (EVS) speech coding modes, each using a bit rate near 13 kb/s. Two EVS Channel Aware (CA) modes were included. Both tests use the Modified Rhyme Test (MRT) protocol and together they comprise over 150,000 trials. The first test used frame erasures targeted at critical consonants for maximum sensitivity and the second used frame erasures generated at random by a two-state Gauss-Markov model. By using these large numbers of MRT trials we found that the CA codec modes offer small but statistically significant speech intelligibility improvements in numerous frame-erasure environments.
Keywords: noise; speech coding; speech quality; modified rhyme test (MRT); packet loss; speech intelligibility; frame erasures; AMR; EVS; channel aware; frame loss
For technical information concerning this report, contact:
Stephen D. Voran
Institute for Telecommunication Sciences
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.