The effect of frequency passband upon the intelligibility of helium-speech in noise

Abstract

Speech spoken after breathing a mixture of helium and oxygen (80%--20%) was combined with white noise and then passed through a variety of bandpass filters. Intelligibility was determined on 16 different groups of 20 listeners each. While intelligibility did not suffer appreciably when frequencies of 300 cs and below were eliminated, the loss of frequencies below 600 cs caused a marked deterioration. Even with severe filtering restrictions of a 600-1200 cs bandpass and a 1-db Speech/Noise ratio, 38% intelligibility was achieved. This indicates that the intelligibility of speech in a helium mixture, as in air, is quite distortion-resistant. The frequency at which high- and low-pass filtering will have equal effects on intelligibility appears to be lower than 1000, in contrast to approximately 1600 cs for speech in air. Reasons for this downward shift are not known. No condition of filtering helium-speech in noise increased its intelligibility.