matlab滤波器代码要点

数字信号处理：

已知通带截止频率fp=5kHz，通带最大衰减ap=2dB，阻带截止频率fs=2kHz，阻带最小衰减as=30dB，按照以上技术指标设计

巴特沃斯低通滤波器：

wp=2*pi*5000;ws=2*pi*12000;Rp=2;As=30;

[N,wc]=buttord(wp,ws,Rp,As,'s');

[B,A]=butter(N,wc,'s');

k=0:511;fk=0:14000/512:14000;wk=2*pi*fk;

Hk=freqs(B,A,wk);

subplot(2,2,1);

plot(fk/1000,20*log10(abs(Hk)));grid on

xlabel('频率（kHz）');ylabel('幅度（dB）')

axis([0,14,-40,5])

切比雪夫1型低通滤波器：

wp=2*pi*3000;ws=2*pi*12000;Rp=0.1;As=60;

[N1,wpl]=cheb1ord(wp,ws,Rp,As,'s'); %cheb1ord,里面的是1，不是L

[B1,A1]=cheby1(N1,Rp,wpl,'s');

subplot(2,2,1);

fk=0:12000/512:12000;wk=2*pi*fk;

Hk=freqs(B1,A1,wk);

plot(fk/1000,20*log10(abs(Hk)));grid on

xlabel('频率（kHz）');ylabel('幅度（dB）')

axis([0,12,-70,5])

椭圆模拟低通滤波器：

wp=2*pi*3000;ws=2*pi*12000;Rp=0.1;As=60;

[N,wpo]=ellipord(wp,ws,Rp,As,'s');

[B,A]=ellip(N,Rp,As,wpo,'s');

subplot(2,2,1);

fk=0:12000/512:12000;wk=2*pi*fk;

Hk=freqs(B1,A1,wk);

plot(fk/1000,20*log10(abs(Hk)));grid on

xlabel('频率（kHz）');ylabel('幅度（dB）')

axis([0,12,-70,5])

p195-14

wp=2*4/80;ws=2*20/80;rp=0.5;rs=45;

[N,wc]=buttord(wp,ws,rp,rs);

[B,A]=butter(N,wc);

[hk,wk]=freqz(B,A);

fk=wk/pi*40;

plot(fk,20*log10(abs(hk)));

axis([0,30,-100,0])

xlabel('频率(kHZ)');ylabel('幅度(db)');grid on P195-16

wp=2*325/2500;ws=2*225/2500;rp=1;rs=40;

[N,wc]=ellipord(wp,ws,rp,rs);

[B,A]=ellip(N,rp,rs,wc);

[hk,wk]=freqz(B,A);

fk=wk/pi*40;

plot(fk,20*log10(abs(hk)));

axis([0,30,-100,0])

xlabel('频率(kHZ)');ylabel('幅度(db)');grid on

P195-15

wp=2*4/80;ws=2*20/80;rp=0.5;rs=45;

[N,wc]=cheb1ord(wp,ws,rp,rs);

[B,A]=cheby1(N,rp,wc);

[hk,wk]=freqz(B,A);

fk=wk/pi*40;

plot(fk,20*log10(abs(hk)));

axis([0,30,-100,0])

xlabel('频率(kHZ)');ylabel('幅度(db)');grid on 切比雪夫低通滤波器

wp=2*pi*3000;ws=2*pi*12000;rp=0.1;as=60;

[N1,wp1]=cheb1ord(wp,ws,rp,as,'s');

[B1,A1]=cheby1(N1,rp,wp1,'s');

subplot(2,2,1);

fk=0:12000/512:12000;wk=2*pi*fk;

hk=freqs(B1,A1,wk);

plot(fk/1000,20*log10(abs(hk)));grid on

xlabel('频率(kHZ)');ylabel('幅度(db)');

axis([0,12,-70,5])

双音频检测

audiofile='test.wav'

[in_audio,fs,bits]=wavread(audiofile); [b,a]=cheby1(5,0.1,0.3);

out_audio=filter(b,a,in_audio);

sound(out_audio,fs,bits);

wavwrite(out_audio,fs,bits,'test_out'); xk1=fft(in_audio,512);

xk2=fft(out_audio,512);

subplot(2,1,1);stem(abs(xk1));

subplot(2,1,2);stem(abs(xk2));

巴特沃斯模拟高通滤波器。

wp=2*pi*4000;ws=2*pi*1000;rp=0.1;as=40; [n,wc]=buttord(wp,ws,rp,as,'s');

[bh,ah]=butter(n,wc,'high','s'); subplot(2,2,1);

fk=0:12000/512:12000;wk=2*pi*fk;

hk=freqs(bh,ah,wk);

plot(fk/1000,20*log10(abs(hk)));grid on xlabel('频率(khz)');ylabel('幅度(db)') axis([0,12,-70,5])

巴特沃斯模拟低通滤波器。

wp=2*pi*5000;ws=2*pi*12000;rp=2;as=30;

[b,a]=butter(n,wc,'s');

k=0:511;fk=0:14000/512:14000;wk=2*pi*fk;

hk=freqs(b,a,wk);

subplot(2,2,1);

plot(fk/1000,20*log10(abs(hk)));grid on

xlabel('频率(khz)');ylabel('幅度(db)')

axis([0,14,-40,5])

巴特沃斯模拟带通滤波器

wp=2*pi*[4000,7000];ws=2*pi*[2000,9000];

[n,wc]=buttord(wp,ws,rp,as,'s');

[bb,ab]=butter(n,wc,'s');

subplot(2,2,1);

fk=0:12000/512:12000;wk=2*pi*fk;

hk=freqs(bb,ab,wk);

plot(fk/1000,20*log10(abs(hk)));grid on

xlabel('频率(khz)');ylabel('幅度(db)')

axis([0,12,-70,5])

巴特沃斯带阻滤波器

wp=2*pi*[2000,9000];ws=2*pi*[4000,7000];rp=1;as=20;

[bsb,asb]=butter(nb,wc,'stop','s');

subplot(2,2,1);

fk=0:12000/512:12000;wk=2*pi*fk;

hk=freqs(bsb,asb,wk);

plot(fk/1000,20*log10(abs(hk)));grid on

xlabel('频率(khz)');ylabel('幅度(db)')

axis([0,12,-70,5])

第14题。巴特沃斯低通滤波器（采样频率80，同代便捷频率4，最大衰减0.5）

wp=2*4/80;ws=2*20/80;rp=0.5;rs=45; [N,wc]=buttord(wp,ws,rp,rs);

[B,A]=butter(N,wc);

[hk,wk]=freqz(B,A);

fk=wk/pi*40;

plot(fk,20*log10(abs(hk)));

axis([0,30,-100,0]);

xlabel('频率(kHz)');ylabel('幅度(dB)')

设计切比雪夫I型和切比雪夫II型模拟低通滤波器。

I型：

wp=2*pi*3000;ws=2*pi*12000;rp=0.1;as=60;

[n1,wp1]=cheb1ord(wp,ws,rp,as,'s');

[b1,a1]=cheby1(n1,rp,wp1,'s');

subplot(2,2,1);

fk=0:12000/512:12000;wk=2*pi*fk;

hk=freqs(b1,a1,wk);

plot(fk/1000,20*log10(abs(hk)));grid on

xlabel('频率(khz)');ylabel('幅度(db)')

axis([0,12,-70,5])

II型：

wp=2*pi*3000;ws=2*pi*12000;rp=0.1;as=60; [n2,wp2]=cheb2ord(wp,ws,rp,as,'s');

[b2,a2]=cheby2(n2,rp,wp2,'s');

subplot(2,2,1);

fk=0:12000/512:12000;wk=2*pi*fk;

hk=freqs(b2,a2,wk);

plot(fk/1000,20*log10(abs(hk)));grid on xlabel('频率(khz)');ylabel('幅度(db)') axis([0,12,-70,5])

切比雪夫I型高通滤波器

wp=2*pi*3000;ws=2*pi*12000;rp=0.1;as=60; [n1,wp1]=cheb1ord(wp,ws,rp,as,'s');

[b1,a1]=cheby1(n1,rp,wp1,'HIGH','s'); subplot(2,2,1);

fk=0:12000/512:12000;wk=2*pi*fk;

hk=freqs(b1,a1,wk);

plot(fk/1000,20*log10(abs(hk)));grid on xlabel('频率(khz)');ylabel('幅度(db)') axis([0,12,-70,5])

设计椭圆模拟低通滤波器。

wp=2*pi*3000;ws=2*pi*12000;rp=0.1;as=60;

[n,wpo]=ellipord(wp,ws,rp,as,'s');

[b,a]=ellip(n,rp,as,wpo,'s');

subplot(2,2,1);

fk=0:12000/512:12000;wk=2*pi*fk;

hk=freqs(b,a,wk);

plot(fk/1000,20*log10(abs(hk)));grid on

xlabel('频率(khz)');ylabel('幅度(db)')

axis([0,12,-70,5])

椭圆带阻滤波器

wp=2*pi*[2000,9000];ws=2*pi*[4000,7000];rp=1;as=20; [ne,wep]=ellipord(wp,ws,rp,as,'s');

[bse,ase]=ellip(ne,rp,as,wep,'stop','s');

subplot(2,2,1);

fk=0:12000/512:12000;wk=2*pi*fk;

hk=freqs(bse,ase,wk);

plot(fk/1000,20*log10(abs(hk)));grid on

xlabel('频率(khz)');ylabel('幅度(db)')

axis([0,12,-70,5])