Harmonic-stochastic excitation (HSX) speech coding below 4 kbit/s

This paper presents an algorithm for encoding speech signals at bit rates below 4 kbit/s based on a mixed harmonic and stochastic modeling of the excitation signal. The algorithm uses robust pitch tracking and efficient voicing analysis to determine the ratios of the harmonic and stochastic components. The harmonic component is synthesized using a bank of bandpass filters while the stochastic component is synthesized using inverse STFT with overlap-and-add. Postfiltering is utilized at the decoder to enhance the quality of synthesized speech. A 2.4 kbit/s version of the algorithm was formally tested and the DAM and DRT scores showed that the coder performance is comparable to that of DoD 4.8 kbit/s Federal Standard FS-1016