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码激励线性预测(CELP)编码在中低速率上与传统的LPC声码器相比可以提供更加自然的语音质量。本文介绍了CELP的基本原理及激励码本的构成。然后提出了在4.8 kbit/s速率上改进话音质量的两种方法:①计算长时预测参数的半闭环搜索法;②激励码本的时变修正法。计算机模拟结果表明,采用这两种方法可使语音质量得到改善。
Code Excited Linear Prediction (CELP) encoding provides a more natural speech quality at lower rates than conventional LPC vocoders. This article describes the basic principles of CELP and excitation codebook structure. Then, two methods to improve speech quality at 4.8 kbit / s rate are proposed: ① semi-closed loop search method to calculate long-term prediction parameters; ② time-varying correction method of excitation codebook. Computer simulation results show that using these two methods can improve the voice quality.