labview设计的巴特沃斯滤波器，参数可自由选择。读取TXT文件数据，显示滤波先后的波形及频谱。labview代码中结合了matlab代码(The Butterworth filter designed by LabVIEW is free to choose parameters. Read the TXT file data, showing the waveform and spectrum of the filter successively. The LabVIEW code com