Human factors evaluation of vocoders for air traffic control environments phase I

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Authors: Bill Belanger
James L. La Due
Annemarie Heinze
Randy Sollenberger, PhD.

La Due, J. L., Sollenberger, R. L., Belanger, B., & Heinze, A. (1997). Human factors evaluation of vocoders for air traffic control environments phase I: Field evaluation (DOT/FAA/CT-TN97/11). Atlantic City International Airport: Federal Aviation Administration William J. Hughes Technical Center.


Communication congestion is a major problem facing the air traffic control system. Vocoders offer a potential solution to this problem by compressing a digitized human speech signal to achieve low bandwidth voice transmissions. Air traffic controllers and pilots must find new systems usable and acceptable before the FAA authorizes implementation. This study compared the performance of two 4.8 kbps vocoders (designated as A and B) with the current analog radio system. Two hundred and seven current air traffic controllers participated in the study. Participants listened to recorded audio messages and provided written responses. The dependent measures included both subjective ratings and objective measures of intelligibility and acceptability. The research design controlled the independent measures of sex of speaker, background noise, and communication equipment. The results indicated that analog radio and vocoder B communications scored subjectively similar. Participants rated radio higher than vocoder B in intelligibility and vocoder B higher than radio in acceptability. They gave Vocoder A the lowest ratings using the subjective scales. An objective message completion test revealed that vocoder B was more intelligible than vocoder A. The results found no generally preferred sex of speaker for vocoder transmissions. There were no major effects of cockpit background noise on the communications.

Updated: May 04, 2012 11:21 AM