Analysis of Speech in a Helium-Oxygen Mixture under Pressure

Tape recordings made in the helium-oxygen atmosphere of the U. S. Navy Sealab II have been analyzed by spectrographic techniques. The divers breathing this gas mixture have an unusual voice quality often characterized as “Donald Duck” speech. The Sealab experiment permitted speech analysis of divers living in such an atmosphere for several days. A study of the recorded data has led to the following observations: (1) formant shifts are responsible for the unusual quality of the helium-oxygen speech; (2) the formant shifts are nonlinear—the first-formant shift being greater than the higher ones; (3) energy associated with fricative sounds has also been observed to shift upward; (4) pitch or fundamental frequency changes are usually not significant; (5) after several days in the preponderantly helium atmosphere of Sealab, changes occurred in the speech quality that made it sound more natural.