对信号进行梅尔倒谱系数特征采集之前的预处理，包括分帧加窗、基于短时能量的双门限判别、除噪、预加重等(The preprocessing of Mel cepstrum coefficients before the signal is carried out, including fr a me windowing, double threshold discrimination based on short-time energy, denoising and pre emphasis)