关键词: 混合激励线性预测（MELP）, 清/浊音（U/V）判决, 语音编码

Abstract: In the Mixed Excitation Linear Prediction（MELP） algorithm，frames with excessive switchings result in quality degradation for synthesized speech，which is a serious problem.In order to solve this problem，a new approach is given to analyze and synthesize the transition segments which are called the transition frames.This can improve the accuracy of parameter estimation and reduce the noise caused by classifying the transition frame simply into U/V frame.A new frame type decision algorithm with dynamic U/V threshold related to the pitch lag is introduced which classifies the speech frame into three types：voiced，unvoiced，and transition.The classifier can reduce the U/V decision errors and avoid excessive switchings between voiced frame and unvoiced frame.An improved bit allocation table is introduced and the PESQ—MOS test shows that the synthesized speech quality has been greatly improved through the new MELP speech coder，especially for high frequency female speakers.

Key words: Mixed Excitation Linear Prediction（MELP）, Unvoiced/Voiced（U/V） decision, speech coder