低通滤波器系数的设置

Lowpass Butterworth Transfer Function
Try This Example
Design a 6th-order lowpass Butterworth filter with a cutoff frequency of 300 Hz, which, for data sampled at 1000 Hz, corresponds to  rad/sample. Plot its magnitude and phase responses. Use it to filter a 1000-sample random signal.

fc = 300;
fs = 1000;

[b,a] = butter(6,fc/(fs/2));
freqz(b,a)