Text normalisation in text-to-speech Synthesis for South African Languages: Native number expansion

Text normalisation in text-to-speech synthesis comprises the segmentation and classification of the incoming text and the subsequent expansion of non-standard words into their standard word, spoken forms. We present a rule-based implementation for the 11 official South African languages that uses native number expansion. We discuss the architecture and performance of the implementation based on examples of cardinal and ordinal numbers, money, dates and times. Although the implementation scores well, it is currently limited to handling non-standard words in isolation. Future work will need to address sentence context in order to normalise the African languages correctly.