18. A speech synthesis system comprising: a voice generation device for processing an acoustic phoneme sequence representative of a text; and a duration modeling device coupled to said voice generation device for receiving phonemes from said voice generation device and providing phoneme durations using a phoneme duration model, wherein said phoneme duration model generates model coefficients by developing a non-exponential functional transformation comprising a root sinusoidal transformation that is controlled in response to a minimum phoneme duration and a maximum phoneme duration, wherein said root sinusoidal transformation is expressed by ##EQU8## 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 wherein said duration modeling device receives said model coefficients from said phoneme duration model and generates at least one phoneme having a duration using a generalized additive model for each phoneme of the received text.
21. The speech synthesis of claim 18, wherein said voice generation device processes the text input using a formant synthesis speech generation model.