1. A method comprising: selecting, via a processor, speech units from a speech unit database, where the speech units are used to generate speech correspond to text; identifying a desired prosodic curve of the speech to be produced from the speech units; identifying an actual prosodic curve of the speech units; decomposing, via a residual-excited linear prediction algorithm, the speech units into residual coefficients and linear predictive coder coefficients; determining a cost of modifying the residual coefficients to yield a determination; modifying, via a pitch synchronous overlap and add algorithm, the residual coefficients, to yield modified residual coefficients based on the determination; combining, via the residual-excited linear prediction algorithm, the modified residual coefficients with the linear predictive coder coefficients, to yield new speech units, such that a new prosodic curve corresponding to the new speech units conforms to the desired prosodic curve; and generating the speech using the new speech units.