巴特沃思滤波器，低通，可自由修改参数进行低通滤波

实现各种典型窗函数的时域与频域特性、已知滤波器条件设计巴特沃思等滤波器、或已知系统函数可求出数字滤波器。-Achieve a variety of typical window function in time domain and frequency domain characteristics, known design Butterworth filter criteria such as filters, or known to the system function can be ob