Formant frequencies, bandwidths, and Qs in helium speech

We used linear prediction analysis to estimate a diver's vocal tract response for isolated vowels spoken in air at 1 atm and in heliox at simulated depths of 54-, 120-, 300-, and 500-m seawater. We specifically measured formant frequency, bandwidth, and Q changes as a function of environment. The formant frequencies shifted upward nonlinearly in helium speech. The formant bandwidths in helium speech increased as much as 14 times their corresponding bandwidths in normal speech. The ratios of formant Qs (helium speech to normal speech) ranges from 0.3 (low formants) to 2 (high formants).