User-Centric Evaluation of Voice over Internet Protocol Codecs for Use in Air Traffic Control Communications

Abstract

In this study researchers performed an assessment of the speech intelligibility of a possible National Airspace System Voice Switch technology, Voice over Internet Protocol (VoIP), to determine its potential suitability in Air Traffic Control (ATC) communications. VoIP is a technique for digital communications that uses standard network protocols and hardware. The study examined the intelligibility difference of five codecs using the Modified Rhyme Test and the Message Completion Task. For the Modified Rhyme Test, codec type had an effect on intelligibility. Relative to uncompressed audio, performance was best and reaction times were fastest for codecs G.711 (bitrate = 64), G.726 (bitrate = 32), and G.729 (bitrate = 8). The subjective intelligibility and acceptability ratings were consistent with the performance data. For the Message Completion Task, intelligibility and acceptability ratings were high, but we found no performance differences. Based on the Modified Rhyme Test findings, we believe the three best-performing codecs may be suitable for ATC communications.