Reconstruction Of Human Speech In a Helium Hyperbaric Atmosphere
R.M. Cram · Offshore Technology Conference · 1979
ABSTRACT As offshore work requirements become more demanding, divers must have the capability to function effectively at greater water depths and under correspondingly greater pressures. In deep water saturation diving systems used for such work, a normal nitrogen/oxygen atmosphere becomes unusable due to its toxic effects. Pioneering work in the field of saturation diving has resulted in the development of helium/oxygen breathing mixtures to replace nitrogen/oxygen combinations. Human speech is altered by this mixture, resulting in effects that range from relatively mild differences at lower hyperbaric pressures to such extreme effects at higher pressures that speech becomes unintelligible and verbal communication impossible. This paper describes quantitatively and qualitatively the effects of a helium/oxygen atmosphere on the human voice and how these effects vary with pressure. From analyzing these effects, a criterion for restoring "helium" speech to normal speech will be developed. An actual hardware implementation of a-linear predictive digital helium speech unscrambler will then be described. The resulting technological advancement should enable the communications aspect of deep diving to keep pace with other developments in this area. The innovative work reflected in this paper is based on an 18 month research and development project conducted by Hydro Products, Inc. for the U.S. Navy. The resulting processor is capable of successfully restoring speech from depths as great as 600 meters. Practical problems associated with a diving environment are also discussed along with the implementation changes necessary to accommodate these difficulties. The technology demonstrated in this paper will allow more efficient and accurate communication between divers and from the diver to the surface, so that necessary off shore inspection and work tasks can be accomplished. Block diagrams and laboratory measurements will be used as illustrations as well as photos of the hardware and test dives. A SUMMARY OF THE PROBLEM Normal atmospheric air is comprised of about 16% oxygen, 78% nitrogen and 6% other gases. As this mixture is compressed and breathed by the human body under pressure during diving, the nitrogen in the air begins to take on toxic properties. The exact nature and severity of these effects vary widely with individuals however, in general the effects worsen with depth, and under certain conditions the results can be fatal. Probably the two most well known effects are:The Bends - Formation of nitrogen bubbles in the bloodstream and joints during rapid decompression.Nitrogen Narcosis - Irrational behavior caused by muddled thinking and in some cases, hallucinations. It has been discovered that substituting helium for nitrogen greatly reduces these effects. The use of helium/oxygen breathing mixtures has resulted in successful tank dives to about 600 meters (2,000 feet). However, the use of helium has its own set of problems. It causes human speech to become distorted and difficult to understand, and at depths below approximately one thousand feet intelligibility is almost lost. Some means of reconstructing "normal" speech out of the "helium" speech must be used.