Nature of helium-speech and its unscrambling

Present status of voice communication in the deep and/or saturation diving situation is unsatisfactory. The use of helium solves physiological problems, but it creates the problem of "helium-speech," the degradation of speech intelligibility. A number of studies on the helium distortions have been reported, and yet the systematic observation and analysis of them have not been carried out. The helium-speech is recorded under the controlled condition. Various aspects of the analysis and observation are made to clarify the nature of helium-speech and to provide the useful data for designing the helium-speech unscrambler. Two types of unscramblers are developed. Analysis-Synthesis type is an extended version of the conventional formant vocoder and is computer-simulated to study various schemes. After a simulation of the Segmentation, Partial-Rejection and Expansion (SPREX) type to get the optimum condition, a digital hard-ware of the SPREX is built.