Voice Communication System Performance in the Presence of Automotive Ignition Noise

This paper reports on recent measurements of voice system performance in a controlled automotive ignition noise environment. At a quiet measurement site in the vicinity of Tucson, AZ, various combinations of from 1 to 12 vehicles of various ages, types, and manufacture were used to provide impulsive interference to four-voice communication system types. These systems were SSB at 23 MHz, with a 10-kHz bandwidth, FM at 75 MHz with a 30-kHz bandwidth, AM at 300 MHz with a 30-kHz bandwidth, and a FM/ PCM system at 900 MHz with a 300-kHz bandwidth. The statistical characterisitcs ( amplitude probability distribution of the received noise envelope and the average crossing-rate characteristics) of the interference were measured simultaneously with the system performance. Two methods were used to measure system performance. An objective measurement using instrumentation termed voice intelligibility analysis system ( VIAS) was used which produces an intelligibility measure called articulation index ( Al). In addition, a subjective method was used employing phonetically balanced word lists and a highly trained listener panel to obtain the articulation score ( AS). One object of the measurements was to ascertain if a relationship exits between Al and AS for impulsive noise, and, indeed, quite good correlation was obtained for all four systems. The results of the system performance measurements and associated results are presented and discussed in detail in this paper.