1. A method for speech synthesis, comprising: providing a segment inventory comprising, for a plurality of speech segments, respective sequences of feature vectors, by estimating spectral envelopes of input speech signals corresponding to the speech segments in a succession of time intervals during each of the speech segments, and integrating the spectral envelopes over a plurality of window functions in a frequency domain so as to determine vector elements of the feature vectors; receiving phonetic and prosodic information indicative of an output speech signal to be generated; selecting the sequences of feature vectors from the inventory responsive to the phonetic and prosodic information; processing the selected sequences of feature vectors so as to generate a concatenated output series of feature vectors; computing a series of complex line spectra of the output signal from the series of the feature vectors; and transforming the complex line spectra to a time domain speech signal for output.