A spectrally mixed excitation (SMX) vocoder with robust parameter determination

Sinusoidal speech coders have been widely studied for low bit rate coding around 4 kbit/s. However, the estimation error of the sinusoidal model parameters would seriously degrade the speech quality. In general, the estimation errors are caused by the effects of various types of speech signal or background noise. In this paper we propose a sinusoidal speech coder with robust parameter determination methods. They consist of spectro-temporal autocorrelation method for robust pitch determination, frequency shifting method for robust voicing level measurement, and residual-spectrum magnitude coding method for spectral magnitude compensation. From the experimental results, we can find the robustnesses of the proposed techniques. In addition, informal listening test of the synthesized speech confirms the effectiveness of the incorporated schemes.