26. The improvement of claim 25 wherein besides said voice source signal, said digital filters receive signals from a noise source means which generates signals representing air turbulence in the voice tract.
26. The improvement of claim 25 wherein besides said voice source signal, said digital filters receive signals from a noise source means which generates signals representing air turbulence in the voice tract. 27. The improvement of claim 26 wherein said one noise source means comprises: an aspiration source means for generating signals representing air turbulence at the vocal cords; and a frication source means using frications from real speech for generating signals representing air turbulence in vocal cavities of the pharynx, mouth and nose.