1. A computer program product for augmenting training data, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to cause the processor to: converting a feature sequence of a source speaker determined from a plurality of utterances within a transcript to a feature sequence of a target speaker under the same transcript; training a speaker-dependent acoustic model for the target speaker for corresponding speaker-specific acoustic characteristics; estimating a mapping function between the feature sequence of the source speaker and the speaker-dependent acoustic model of the target speaker; and mapping each utterance from each speaker in a training set using the mapping function to multiple selected target speakers in the training set.