A preprocessing method for pitch smoothing and voicing-level improvement

In low bit rate speech coders, pitch is usually transmitted once per frame and, when needed, the intermediate pitch values are obtained by interpolation between two adjacent pitch values. Although pitch usually evolves slowly, sometimes it has nonlinear variation and the estimated pitch differs from the real one. This affects the synthesised speech quality. We propose to use a preprocessor, which modifies the residual speech signal such that the pitch period evolves more smoothly without distorting perceptual speech quality. Thus, the pitch and the voicing level can be determined correctly.