Helium speech unscramblers--A critical review of the state of the art (original) (raw)

The development of saturation diving has enabled man to work in t h e sea at great depths and for long periods of time. This advance has resulted, in part, as a consequence of the substitution of helium for nitrogen in breathing gas mixtures. However, the utilization of HeOz breathing mixtures at high ambient pressures has caused problems in speech communication; in turn, electronic aids have been developed to improve diver communication. These helium speech unscramblers attempt to process variously the grossly unintelligible speech resulting from the effects of helium-oxygen breathing mixtures and ambient pressure, and to reconstruct such signals in order to provide adequate voice communication. This paper presents a discussion of the effects of He02/P on speech and then describes some of the techniques used to "unscramble" the distorted speech. Included among the techniques are: 1) frequency subtraction; 2) tape recorder playback; 3) vocoder approaches; 4) digital coding; and 5) convolution processing. In addition, a generalized evaluation of these approaches is included.