An improved correction formula for the estimation of harmonic magnitudes and its application to open quotient estimation

Many voice quality parameters, such as the open quotient (OQ), depend on an accurate estimate of the source spectrum. It is known that OQ, for example, is correlated with the magnitude difference of the first two harmonics (H₁-H₂) of the speech source spectrum. In order to compare OQ estimates across different vocal tract configurations a magnitude correction is achieved by removing the influence of vocal tract resonances. The improved correction described in this paper is inspired by a correction formula of H. M. Hanson (see Glottal characteristics of female speakers, PhD. dissertation, Harvard university, Cambridge, MA, 1995). The new correction formula accounts for the bandwidths of all the vocal tract resonances, and most importantly, is not limited to the analysis of non-high vowels. H₁-H₂ estimates, using the proposed technique with synthesized vowels generated with the Liljencrants-Fant (LF) and the KLGLOTT88 models, are very accurate.