In Speect the utterance and feature processors (as explained in the introduction) are the most important aspect of TTS. The Speect Engine provides the basic data structures and controls the utterance processor pipeline defined by the voice utterance types. Utterance processors modify the utterance using the HRG structures, extracting features from items with feature processor paths.
Utterance and feature processors are defined as plug-ins and are described in more detail in the respective API’s: