1. A method comprising: generating a plurality of input models representing an input by using a statistical model synthesizer to statistically model the input; determining, using a processor, a speech unit sequence representing at least a portion of the input by using the input models to influence selection of one or more pre-recorded speech units having parameter representations; identifying one or more bad units in the speech unit sequence, wherein determining the speech unit sequence and identifying one or more bad units in the speech unit sequence are performed substantially simultaneously; and replacing the identified one or more bad units with one or more parameters generated using the statistical model synthesizer.