The effective second formant F2´ and the vocal tract front-cavity

The authors advance the hypothesis that the equivalent perceptual second formant F2´ carries information about the front cavity of the vocal tract. They note a previous result that peaks found by perceptually based linear predictive (PLP) analysis closely track the F2´. The authors recall P. Mermelstein´s (1967) observation of the relative invariance of the front cavity shape and size in vowels synthesized to maintain a constant F-pattern under variations of the vocal tract length. They show by tracing X-rays that humans with radically different vocal tract lengths tend to preserve the front cavity shape and size when producing vowels with identical phonetic values. Articulatory synthesis with variable vocal tract lengths is used to demonstrate that the F2´ from the PLP model follows the resonance frequency of the front cavity