8. A computer program product comprising at least one computer-readable storage medium having computer-readable program code portions stored therein, the computer-readable program code portions comprising: a first executable portion for extracting a feature indicative of a property of a vocal tract of a speaker from each of training source speech and training target speech; a second executable portion for defining sub-feature units with respect to the feature for both the training source speech and the training target speech to generate training source speech sub-feature units and training target speech sub-feature units, respectively; and a third executable portion for performing voice conversion of source speech to target speech based on the conversion of the sub-feature units to corresponding target speech sub-feature units using a conversion model trained with respect to converting the training source speech sub-feature units to the training target speech sub-feature units.
8. A computer program product comprising at least one computer-readable storage medium having computer-readable program code portions stored therein, the computer-readable program code portions comprising: a first executable portion for extracting a feature indicative of a property of a vocal tract of a speaker from each of training source speech and training target speech; a second executable portion for defining sub-feature units with respect to the feature for both the training source speech and the training target speech to generate training source speech sub-feature units and training target speech sub-feature units, respectively; and a third executable portion for performing voice conversion of source speech to target speech based on the conversion of the sub-feature units to corresponding target speech sub-feature units using a conversion model trained with respect to converting the training source speech sub-feature units to the training target speech sub-feature units. 12. A computer program product according to claim 8 , further comprising a fourth executable portion for selecting the source speech from a plurality of synthetic voices based on the target speech.