bartle自功率谱密度分析，对于直接法的功率谱估计，当数据长度N太大时，谱曲线起伏加剧，若N太小，谱的分辨率又不好，因此需要改进。-Bartle since the power spectral density analysis, for the direct method of power spectrum estimation, when the data length N is too large, the spectrum curve of the ups and downs, if N is too small, the resolution of the spectrum and is not good, so need to improve.