4. The method of claim 1 wherein optimizing the graphoneme model comprises performing discriminative training of graphoneme model parameters using the acoustic data.
1. A method performed by a computer comprising storage and a processor, the method comprising: modeling acoustic data, a phoneme sequence, a grapheme sequence and an alignment between the phoneme sequence and the grapheme sequence to provide a graphoneme model stored in the storage; and retraining, by the processor, a grapheme to phoneme model usable in speech recognition by optimizing the graphoneme model using acoustic data stored in the storage.