基于GMM的甚低码率语音编码器

提出了一种新颖的基于高斯混合模型(GMM)的甚低码率语音编码系统.该编码器利用GMM对短时语音谱包络进行拟合的方法来对语音进行参数化表示.编码时,语音经预处理、分帧加窗后,再经FFT分析得到分帧语音的信号频谱,并获得平滑谱包络.然后采用GMM对谱包络进行拟合,用GMM参数(均值、方差、权重)对语音谱加以表示.由于GMM参数较少,从而可以使得码率甚低.解码时,根据编码逆运算生成谱包络,浊音信号利用正弦模型加以合成,清音信号经IFFT合成.实验仿真结果表明:该编码器在传输码率降低到2.35 kb/s时,仍可获得音质令人满意的解码语音.

A Very Low Bit-rate Speech Coder Based on GMM

A novel very low bit-rate speech coder based on Gaussian mixture model(GMM),which is used to parameterize the short-time speech spectrum envelope,is proposed in this paper.In the coding procedure,speech signal is firstly pre-emphasized and segmented.Secondly,the segmented speech is transformed to spectrum domain and the spectrum envelope of the segmented speech is obtained.Then the spectrum envelope is parameterized by GMM.So the segmented speech is represented by the means,covariances and mixture weights of GMM.In the decoding procedure,the spectrum envelope of segmented speech is reconstructed with the inverse method of the coding.Then the speech is synthesized based on the reconstructed spectrum envelope,in which the voiced speech is synthesized by sinusoid model and the unvoiced speech is just synthesized by inverse FFT.Since the segmented speech can be represented by very few parameters of GMM,the bit-rate of the coder is very low.The result of the experiment shows that the proposed speech coder presents a good performance.The quality of the synthesized speech is still satisfying when the bit-rate of the coder is reduced to 2.35 kb/s.