Voice Over Internet Protocol: Speech Intelligibility Assessment

In this study, the authors examined the speech intelligibility of five codecs and parameter settings to determine their suitability for Air Traffic Control use. These codecs (g711r64, g726r32, g729r8, g723r53, and g726r16) convert analog communications to digital communications. Standard intelligibility tests were used − the Modified Rhyme Test (MRT) and the Message Completion Task (MCT) − to examine intelligibility differences. For the MRT, codec type had an effect on intelligibility. Performance in an uncompressed audio condition was the best, followed by codecs g711r64 and g726r32, then g729r8, and then g723r53 and g726r16, respectively. Reaction times were consistent with the performance data, with the better performing codecs having shorter reaction times. Subjective intelligibility and acceptability ratings matched the performance and reaction time data. For the MCT, the intelligibility and acceptability ratings for all codecs were high, but no clear pattern was found in the performance data. The authors recommend that the National Airspace System Voice Switch (NVS) program further evaluate the three best performing codecs, g711r64, g726r32, and g729r8. These codecs delivered the best performance, the shortest reaction times, and the most positive feedback. It is also recommended that the NVS Program Office investigate the effect of channel noise, ambient noise, and level of network utilization on the intelligibility of different codecs.

  • Record URL:
  • Corporate Authors:

    Federal Aviation Administration

    William J. Hughes Technical Center, Atlantic City International Airport
    Atlantic City, NJ  United States  08405

    Federal Aviation Administration

    800 Independence Avenue, SW
    Washington, DC  United States  20591
  • Authors:
    • Friedman-Berg, Ferne
    • Allendoerfer, Kenneth
    • Deshmukh, Atul
  • Publication Date: 2009-12


  • English

Media Info

  • Media Type: Digital/other
  • Edition: Technical Note
  • Features: Appendices; Figures; References; Tables;
  • Pagination: 36p

Subject/Index Terms

Filing Info

  • Accession Number: 01526327
  • Record Type: Publication
  • Report/Paper Numbers: DOT/FAA/TC-TN-09/04
  • Files: TRIS, ATRI, USDOT
  • Created Date: Apr 28 2014 10:46AM