MODEL-MAPPING BASED VOICE CONVERSION SYSTEM A Novel Approach to Improve Voice Similarity and Naturalness using Model-based Speech Synthesis Techniques

In this paper we present a novel voice conversion application in which no any knowledge of source speakers is available, but only sufficient utterances from a target speaker and a number of other speakers are in hand. Our approach consists in two separate stages. At the training stage, we estimate a speaker dependent (SD) Gaussian mixture model (GMM) for the target speaker and additionally, we also estimate a speaker independent (SI) GMM by using the data from a number of speakers other than the source speaker. A mapping correlation between the SD and the SI model is maintained during the training process in terms of each phone label. At the conversion stage, we use the SI GMM to recognize each input frame and find the closest Gaussian mixture for it. Next, according to a mapping list, the counterpart Gaussian of the SD GMM is obtained and then used to generate a parameter vector for each frame vector. Finally all the generated vectors are concatenated to synthesize speech of the target speaker. By using the Proposed model-mapping approach, we can not only avoid the over-fitting problem by keeping the number of mixtures of the SI GMM to a fixed value, but also simultaneously improve voice quality in terms of similarity and naturalness by increasing the number of mixtures of the SD GMM. Experiments showed the effectiveness of this method.