说明：  这个是用来进行基频检测的，目前做的最好的应该数Paul的基频提取算法了，误差可以小于万分之五。该源代码的算法是我根据Paul的算法修改得到，省略了插值部分，所以误差在百分之五以内，但是在实际工作中已经足够了。
(is for the frequency of detection, so the best should be the number of frequency Paul extraction algorithm, can be less than prior error. The source code for the algorithm is based on the algorithm Paul to be amended, omitted the interpolation part, the error within 5%, but the actual work has been sufficient.)