1. Speech synthesis apparatus comprising: a language generator responsive to input information indicative of at least the content of a desired speech output, to generate a corresponding text-form utterance; a text-to-speech converter for converting text-form utterances received from the language generator into speech form; and an assessment arrangement for assessing the overall quality of the speech form produced by the text-to-speech converter from an input text-form utterance whereby to selectively produce a modification indicator when it determines that the current speech form is inadequate; the language generator being responsive to the assessment arrangement producing a said modification indication, to generate a new version of the text-form utterance concerned.