Evaluation of methods for parameteric formant transformation in voice conversion

This paper explores methods of estimation and mapping of parametric formant-based models for voice transformation. The main focus is the transformation of the parameters of a model of the vocal tract of a source speaker to a target speaker. The vocal tract parameters are represented with the linear prediction (LP) model coefficients and the associated formant frequencies, bandwidths, intensities and their temporal trajectories. Two methods are explored for vocal tract (formant) mapping. The first method is based on nonuniform frequency warping and the second is based on pole rotation. Both methods transform all parameters of the formants (frequency, bandwidth and intensity). In addition, the factors that affect the selection of the warping ratios for the mapping functions are presented. Experimental evaluation of voice morphing based on parametric models are presented.