A mixed-source model for speech compression and synthesis

This paper presents an excitation source model for speech compression and synthesis, which allows for a degree of voicing by mixing voiced (pulse) and unvoiced (noise) excitations in a frequency-selective manner. The mix is achieved by dividing the speech spectrum into two regions, with the pulse source exciting the low-frequency region and the noise source exciting the high-frequency region. A parameter Fcdetermines the degree of voicing by specifying the cut-off frequency between the voiced and unvoiced regions. For speech compression applications, Fccan be extracted automatically from the speech spectrum and transmitted. Experiments using the new model indicate its power in synthesizing natural sounding voiced fricatives, and in largely eliminating the "buzzy" quality of vocoded speech. A functional definition of buzziness and naturalness is given in terms of the model.