利用DFT分析离散信号频谱的实验。利用FFT分析信号 x[k]=cos(3pik/8 +pi/4 ) 的频谱；确定DFT计算的参数，绘出其频谱；并进行理论值与计算值比较。-DFT analysis of discrete signal spectrum utilization experiments. Analysis using FFT signal x [k] = cos (3pik/8+ pi/4) of the spectrum　determine the parameters of DFT calculations, draw its spectrum　and comparing the theoretical and calculated values.