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在低速率声码器中,对激励信号的描述直接影响重建语音的质量.为了改善音质,提出一种基于语音截止频率的声码器激励模型.该模型编码时通过语音截止频率将激励谱分成谐波和噪声2个子带,谐波子带的激励谱幅度引入离散余弦变换变维模型进行描述,语音截止频率进行4 bit非线性量化.解码时将恢复出的谐波子带激励谱幅度进行傅里叶反变换,噪声子带则由白噪声进行以语音截止频率为阻带截止频率的高通滤波,最后由谐波子带和噪声子带叠加出激励.实验结果表明,该模型提高了全带激励谱幅度和谐波噪声成分的描述精度,可使重建语音的音质得以明显改善,主客观指标更优,对男声更为突出.
In the low-rate vocoder, the description of the excitation signal directly affects the quality of the reconstructed speech.In order to improve the sound quality, a vocoder excitation model based on the speech cutoff frequency is proposed, which divides the excitation spectrum into Harmonic and noise 2 sub-bands, the excitation sub-band excitation spectrum amplitude introduced discrete cosine transform dimensional model to describe the speech cut-off frequency of 4 bit non-linear quantization will be restored when decoding the harmonic sub-band excitation spectrum amplitude The inverse Fourier transform and the noise sub-band are high-pass filtered by the white noise at the cut-off frequency of the stop-band and finally the excitation is superimposed by the harmonic sub-band and the noise sub-band.The experimental results show that the model improves the overall With the description of excitation spectrum amplitude and harmonic noise components, the sound quality of reconstructed speech can be obviously improved, the subjective and objective indicators are better, and the male voice is more prominent.