数字滤波器的C语言实现，其中包括低通，带通，高通滤波器，还有巴特沃斯滤波器的实现-The C language realization of digital filters, including low-pass, band pass, high pass filter, as well as the realization of Butterworth filter

IIR 巴特沃斯滤波器实现（低通、高通、带通、带阻）, 掌握数字滤波器的设计过程.-IIR Butterworth filter implementations (low pass, high pass, band pass, band stop), master of the digital filter design process.