A SINGLE DSP SYSTEM FOR HIGH-QUALITY ENHANCEMENT OF DIVERS SPEECH

The development of saturation diving in civil and defense applications has enabled man to work in the sea at great depths and for long perio ds of time. This advance has resulted, in part, as a consequence of th e substitution of helium for nitrogen in breathing gas mixtures. Howev er, utilization of HeO2 breathing mixture at high ambient pressures ha s caused problems in speech communication; in turn, helium speech enha ncement systems have been developed to improve diver communication. Th ese speech unscramblers attempt to process variously the grossly unint elligible speech resulting from the effect of breathing mixtures and a mbient pressure, and to reconstruct such signals in order to provide a dequate Voice communication. It is known that the glottal excitation i s quasi-periodic and the vocal tract filter is quasi-stationary. Hence , it is possible to use an auto regressive modelisation to restore spe ech intelligibility in hyperbaric conditions. Corrections are made on the vocal tract transfer function, either in the frequency domain, or directly on the autocorrelation function. A spectral subtraction or no ise reduction may be added to improve speech quality. A new VAD enhanc ed helium speech unscrambler is proposed for use in adverse conditions or in speech recognition. This system, implementable on single chip D SP of current technology, is capable to work in rear time.