13. A method according to claim 12 , wherein: for each repletion, p and q are such that the partial time series of first speech parameter vectors {x i } p . . . q , the partial time series of second speech parameter vectors {Δ i } p . . . q and the partial time series of corresponding third speech parameter vectors {y i } p . . . q overlap each other by a non-zero number of vectors; and the combining the plurality of successive partial time series of third speech parameter vectors comprises forming a non-overlapping time series of output speech parameter vectors {ŷ i } 1 . . . m , including, for each of at least some of the plurality of successive partial time series of third speech parameter vectors: applying to final vectors of the partial time series of third speech parameter vectors a first scaling function that decreases with time; applying to initial vectors of an immediately successive partial time series of third speech parameter vectors a second scaling function that increases with time; and adding together the scaled overlapping final and initial vectors.
13. A method according to claim 12 , wherein: for each repletion, p and q are such that the partial time series of first speech parameter vectors {x i } p . . . q , the partial time series of second speech parameter vectors {Δ i } p . . . q and the partial time series of corresponding third speech parameter vectors {y i } p . . . q overlap each other by a non-zero number of vectors; and the combining the plurality of successive partial time series of third speech parameter vectors comprises forming a non-overlapping time series of output speech parameter vectors {ŷ i } 1 . . . m , including, for each of at least some of the plurality of successive partial time series of third speech parameter vectors: applying to final vectors of the partial time series of third speech parameter vectors a first scaling function that decreases with time; applying to initial vectors of an immediately successive partial time series of third speech parameter vectors a second scaling function that increases with time; and adding together the scaled overlapping final and initial vectors. 20. A method according to claim 13 , wherein the first scaling function comprises a first half of a Hanning function, and the second scaling function comprises a second half of a Hanning function.