Acoustic tube analysis of formant bandwidths and frequencies in helium speech

We use the lossy electric transmission-line analog model of the vocal tract to study the acoustics of speech produced in a hyperbaric helium-oxygen atmosphere. The analysis extends previous work by including more completely the effects of the wall vibration, glottal, and radiation impedances, and by analyzing the formant bandwidths and amplitudes in addition to the formant frequencies. It shows that (1) the classic Fant and Lindquist formula somewhat overstates the formant frequency shift when glottal and radiation effects are included; (2) the lower formant bandwidths increase by much more than commonly assumed; and (3) the upper formant amplitudes are higher relative to the lower formants in helium speech than in normal speech. These results are useful in developing advanced helium speech enhancement algorithms.