Transformation of speaker characteristics for voice conversion

The paper presents a voice conversion method based on analysis and transformation of the characteristics that define a speaker's voice. Voice characteristic features are grouped into three main categories: (a) the spectral features at formants; (b) the pitch and intonation pattern; (c) the glottal pulse shape. Modelling and transformation methods for each group of voice features are outlined. The spectral features at formants are modelled using a two-dimensional phoneme-dependent HMM. Subband frequency warping is used for spectrum transformation where the subbands are centred on estimates of formant trajectories. The F0 contour, extracted from autocorrelation-based pitchmarks, is used for modelling the pitch and intonation patterns of speech. A PSOLA based method is used for transformation of pitch, intonation patterns and speaking rate. Finally a method based on deconvolution of the vocal tract is used for modelling and mapping of the glottal pulse. The experimental results present illustrations of transformations of the various characteristics and perceptual evaluations.