《DSP using MATLAB》示例Example7.24

代码：

ws1 = 0.2*pi; wp1 = 0.35*pi; wp2 = 0.65*pi; ws2 = 0.8*pi;
Rp = 1.0; As = 60;
[delta1, delta2] = db2delta(Rp, As);

f = [ws1, wp1, wp2, ws2]/pi; m = [0, 1, 0]; delta = [delta2, delta1, delta2];

[N, f, m, weights] = firpmord(f, m, delta); 
N

h = firpm(N, f, m, weights);
[db, mag, pha, grd, w] = freqz_m(h, [1]);
delta_w = 2*pi/1000; 
ws1i = floor(ws1/delta_w)+1; wp1i = floor(wp1/delta_w)+1;
ws2i = floor(ws2/delta_w)+1; wp2i = floor(wp2/delta_w)+1;

Asd = -max(db(1:1:ws1i))


N = N +  1
h = firpm(N, f, m, weights);

[db, mag, pha, grd, w] = freqz_m(h, [1]);
Asd = -max(db(1:1:ws1i))


N = N +  1
h = firpm(N, f, m, weights);

[db, mag, pha, grd, w] = freqz_m(h, [1]);
[Hr, ww, a, L] = Hr_Type1(h);
Asd = -max(db(1:1:ws1i))

M = N + 1

　　运行结果：

     当Asd超过给定的60dB就停止。