### 14.4 Utterance modules ¶

The module is the basic unit that does the work of synthesis. Within Festival there are duration modules, intonation modules, wave synthesis modules etc. As stated above the utterance type defines the set of modules which are to be applied to the utterance. These modules in turn will create relations and items so that ultimately a waveform is generated, if required.

Many of the chapters in this manual are solely concerned with particular modules in the system. Note that many modules have internal choices, such as which duration method to use or which intonation method to use. Such general choices are often done through the `Parameter` system. Parameters may be set for different features like `Duration_Method`, `Synth_Method` etc. Formerly the values for these parameters were atomic values but now they may be the functions themselves. For example, to select the Klatt duration rules

    (Parameter.set 'Duration_Method Duration_Klatt)

This allows new modules to be added without requiring changes to the central Lisp functions such as `Duration`, `Intonation`, and `Wave_Synth`.