1. A method for converting an input linguistic description into a speech waveform comprising: deriving at least one target unit sequence corresponding to the input linguistic description; assigning in a waveform unit database one or more waveform units to each target unit of the at least one target unit sequence; selecting for the at least one target unit sequence a plurality of alternative waveform unit sequences approximating the at least one target unit sequence, using the one or more waveform units assigned to each target unit of the at least one target unit sequence; concatenating the alternative waveform unit sequences to form alternative speech waveforms; and presenting the alternative speech waveforms to an operating person and enabling the choice of one of the presented alternative speech waveforms.