An improved hyperbaric speech transcoder

This paper deals with a technique for improving the restoration of the spec tral properties of the speech of deep-sea divers operating under Various co nditions of gas mixtures and diving depths. The method used here is based a n the modified digital channel vocoder. Intelligibility problems linkes to hyperbaric speech are briefly described. The limits of the usual channel vo coder for this kind of correction are also discussed, particularly those co ncerning the frequency domain of application of Fant-Lindquist's formant la w. In some cases, the use of this law in its indirect form may lead to the calculation of the square root of a negative number. Solutions are then put forward, and hyperbaric speech records from "Hydra IV" (physiological expe riments using pressurised helium diving) are processed to validate the prop osed method.