《DSP using MATLAB》示例Example7.23

代码：

wp = 0.2*pi; ws = 0.3*pi; Rp = 0.25; As = 50;
[delta1, delta2] = db2delta(Rp, As);

[N, f, m, weights] = firpmord([wp, ws]/pi, [1, 0], [delta1, delta2]);

N
f
m
weights

h = firpm(N, f, m, weights);
[db, mag, pha, grd, w] = freqz_m(h, [1]);

delta_w = 2*pi/1000; wsi = ws/delta_w+1; wpi = wp/delta_w;
Asd = -max(db(wsi:1:501))

N = 46;
h = firpm(N, f, m, weights);
[db, mag, pha, grd, w] = freqz_m(h, [1]);
[Hr, ww, b, L] = Hr_Type2(h);

delta_w = 2*pi/1000; wsi = ws/delta_w+1; wpi = wp/delta_w;
Asd = -max(db(wsi:1:501))

M = N + 1

　　运行结果：

注意，我们是在最大阻带衰减As的值超过给定的50dB后停止迭代的，最优的M=47。这个值要比采用窗函数（Kaiser窗时M=61）和频率采样方法（M=60）

要小得多。