6. A non-transitory computer-readable storage medium having stored thereon instructions, which when executed by a processor result in one or more concatenative speech synthesis operations, the operations comprising: accessing, using one or more computing devices, a plurality of speech synthesis units from a speech database; determining a similarity between the plurality of speech synthesis units, wherein determining the similarity is based upon, at least in part, a similarity factor; retrieving two or more speech synthesis units having the similarity; and pruning at least one of the two or more speech synthesis units based upon, at least in part, the similarity, wherein pruning is based upon, at least in part, a delta unit appearance frequency “DUAF” technique and wherein the DUAF is based upon, at least in part, a change in a unit appearance frequency and a change of the similarity factor.
6. A non-transitory computer-readable storage medium having stored thereon instructions, which when executed by a processor result in one or more concatenative speech synthesis operations, the operations comprising: accessing, using one or more computing devices, a plurality of speech synthesis units from a speech database; determining a similarity between the plurality of speech synthesis units, wherein determining the similarity is based upon, at least in part, a similarity factor; retrieving two or more speech synthesis units having the similarity; and pruning at least one of the two or more speech synthesis units based upon, at least in part, the similarity, wherein pruning is based upon, at least in part, a delta unit appearance frequency “DUAF” technique and wherein the DUAF is based upon, at least in part, a change in a unit appearance frequency and a change of the similarity factor. 7. The non-transitory computer-readable storage medium of claim 6 , wherein the pruning is based upon, at least in part, a delta unit appearance frequency technique and a unit appearance frequency technique.