Helium speech enhancement using the short-time Fourier transform

Speech produced in a hyperbaric helium-oxygen atmosphere suffers a variety of distortions which render it virtually unintelligible. This paper describes a new system for helium speech enhancement based on a short-time Fourier transform signal representation. The algorithm is robust, allows nonlinear warping of the spectral envelope, and includes provisions for generating the enhanced speech at a reduced sampling rate. Noise reduction by spectral subtraction can be included, and the algorithm is amenable to real-time implementation on an array processor. A review of helium speech phenomena is included to motivate the design, and a new result for the behavior of formant bandwidths is given. The results of formal intelligibility tests are reviewed, These tests show an improvement in intelligibility from about 40 to 70 percent. The tests also show that the noise reduction scheme is detrimental to intelligibility, but fail to conclusively resolve the importance of a non-linear formant frequency shift.