8. An apparatus for generating speech from text, comprising: storage means for storing a set of decision tree based context-dependent phoneme-based units of a target speaker, wherein a central phoneme-based unit is selected from a group consisting of a phoneme and a diphone, wherein each context-dependent phoneme-based unit is arranged based on context of at least one immediately preceding and succeeding phoneme-based unit, and wherein at least one of the context-dependent phoneme-based units represents other non-stored context-dependent phoneme-based units of similar sound due to similar contexts; a text analyzer for obtaining a string of phonetic symbols representative of a text to be converted to speech; and a concatenation module for selecting stored decision tree base context-dependent phoneme-based units from the set of decision tree based context-dependent phoneme-based units based on the context of the phonetic symbols and synthesizing the selected context-dependent phoneme-based units to generate speech corresponding to the text.
9. The apparatus of claim 8 wherein the phoneme-based unit comprises a phoneme and wherein the context-dependent phoneme-based unit is a triphone, a phoneme in the context of the one immediately preceding and succeeding phonemes.