Speech intelligibility assessment in a helium environment

The purpose of this study was to compare the appropriateness and effectiveness of the speech perception in noise (SPIN) test and the Griffiths version of the modified rhyme test (GMRT) in assessing Navy divers' speech understanding using communication systems containing different helium speech unscramblers (HSUs), one of which produces, by subjective observations, more intelligible output than the other. Divers participating in a saturation deep dive and a group of nondivers using digital audio tape recordings of the stimuli used by the divers were tested. Mean percent correct scores on the SPIN and GMRT lists within two listening conditions (taped, topside-diver and live-voice, diver-diver) were almost identical. Listeners scored better on both tests in the topside-diver condition than in the diver-diver condition. The majority of the SPIN errors were on low-predictability items that are void of context. Context clearly played a role in measuring the performance of these subjects, at least for the SPIN test. No significant differences were measured between the two HSUs, although a trend was seen favoring one HSU over the other for the divers. These results have theoretical as well as practical value for measuring the quality and intelligibility of helium speech enhancement systems.