1. A computer readable medium storing a computer program to perform method steps for execution by a processor, the method steps comprising: generating a synthetic waveform for each of N textual transcriptions of an original waveform, wherein N is greater than 1 and the N textual transcriptions are generated by a speech recognition system and represent N-best textual transcription hypotheses of the original waveform; for each synthetic waveform, time-aligning feature vectors of the synthetic waveform with feature vectors of the original waveform at a phoneme level; computing a mean of the feature vectors which align to each phoneme for the original waveform and the synthetic waveform; computing a distance measure between each phoneme mean of the original waveform and the synthetic waveform; summing the distance measures to generate an overall distance measure representing a distance between the original waveform and the synthetic waveform; comparing scores based on the overall distance measure between the synthetic waveform and the original waveform, an acoustic model score of a corresponding textual transcription of the synthetic waveform, and a language model score of the corresponding textual transcription to determine a corresponding one of the N-best textual transcriptions; and selecting for output the determined N-best textual transcription.