ITU-T G.729與G.723.1編碼參數之有效率轉碼技術

An Efficient Transcoding Scheme in Parameters for ITU-T G.729 and G.723.1 Codec

本文提出使用於G.729(8kbit/s)與G.723.1(6.3kbit/s)語音編碼器之間低計算複雜度的轉碼演算法。以三個G.729 主音框對應一個G.723.1 主音框，轉碼演算法包含四個部份：分別為以線性內插技術轉換線頻譜對與基週參數、快速適應性增益碼簿搜尋、快速隨機碼簿搜尋。快速適應性增益碼簿搜尋方法是事先利用語音殘值訊號來預測，五階閉迴路基週適應性增益碼向量，如此可減少適應性增益碼簿編碼所需的計算量。利用激發脈衝能量函數來預估篩選隨機激發脈衝可能位置，以進一步降低隨機碼簿搜尋所需之計算量。經實驗分析，本文所提出之低計算複雜度轉碼技術，與串聯法相比G.723.1 編碼過程約可減少84.87%的計算量及保持良好的語音品質且擁有較少的編碼延遲時間。

We proposed an efficient method of converting speech codec formats between the G.729 and G.723.1 speech codec. The G.729 three frames is converted to one frame of the G.723.1, transcoding is completed through four processes： LSP and pitch conversions are used to linear interpolation processing, respectively, fast adaptive-codebook search processing adopt to predict the range of adaptive-codebook gain in the G.723.1, and a fast stochastic excitation pulses estimates method. Simulation results show that the proposed method is able to reduce the computation complexity about 84.87% with shorter delay than the tandem. And the perceptual speech quality (PESQ) evaluated better than the latter.