1. A method comprising: applying linear prediction to a set of source sounds to generate a source feature vector and to a set of target sounds to generate a target feature vector; aligning the source feature vector with the target feature vector to generate a joint variable; and training a mixture model based on the joint variable by (1) estimating a mixture mean vector of the joint variable, the mixture mean vector comprising a plurality of mixture mean pairs and (2) generating a mixture specific warping function for each of the plurality of mixture mean pairs.