自适应后滤波技术在波形内插编码算法中的应用

本文将自适应后滤波技术引入3kbps特征波形内插语音编码算法中,在解码端级联短时后滤波、频谱倾斜补偿、长时后滤波及自动增益控制四个模块。通过理论分析及主观听音测试来合理设置滤波系数,使其随着语音帧的特性自适应改变。经后滤波处理的输出语音信号频谱在共振峰及谐波处频率成分得到加强,而谱谷值处噪声被削弱,同时保证了滤波前后的信号能量基本保持不变,且不引入频谱倾斜。实验结果表明,本文的3kbps波形内插编码器合成语音经过自适应后滤波处理后量化噪声明显减少,语音质量得到改善。

Adaptive Postfilter used in Waveform Interpolation Speech Coding

This paper combines adaptive postfilter technique with 3kbps characteristic waveform interpolation (CWI) algorithm. The decoder is in tandem with short-term postfilter,spectral tilt compensation,long-term postfilter and automatic gain control.The param- eters of postfilter are set properly by theory analysis and subjective listening test and are varied adaptively with the speech frame feature. The coding speech is processed and keeps the energy by the postfiter with attenuation between formant peaks and pitch harmonic peaks but without a spectral tilt.The experiment results show that after postfiltering the quantization noise of the 3kbps CWI synthesized speech is obviously reduced and the speech quality is improved.