1. A method for producing synthetic speech comprising: receiving text into a processor; processing the text using a phoneme duration model, the phoneme duration model produced by developing a non-exponential functional transformation form for use with a generalized additive model, wherein the non-exponential functional transformation is expressed by ##EQU3## where x comprises one or more of a plurality of contextual factors influencing the duration of a phoneme, A is the minimum phoneme duration observed in training data, B is the maximum phoneme duration observed in training data, .alpha. controls the amount of shrinking and expansion on either side of a main inflection point, and .beta. controls the position of the main inflection point; and generating speech signals representative of the received text.