对连续的单一频率离散序列 ，即k=8。 按采样频率 采样，截取长度N分别选N =20和N =16，观察其DFT结果的幅度谱。 -Discrete to continuous sequence of single frequency, ie k = 8. According to the sampling frequency sampling, truncation length N = 20 N, respectively, and selected N = 16, observed the results of its DFT magnitude spectrum.