输入一个含有噪声的信号，使用fft将频谱显示出来、并可输入低通、高通，带通滤波的数值，结果立刻可现，不过是基于evc的程序，会vc的一看即明白-Enter a noisy signal, using fft the spectrum display, and can enter the low-pass, high pass, band-pass filter value, the results are immediately available, but the procedure is b