filter.m

1)生成2KHz和8KHz的混合信号

fs=20000;fpass=4000;fstop=5000;
fc=(fpass+fstop)/2;width=2*pi*(fstop-fpass)/fs;
M=ceil(6.6*pi/width)+1
B=0.5;
n=0:M-1;

lp_n=n-(M-1)/2+eps;
hn=sin(2*pi*lp_n*fc/fs)./(pi*lp_n);

wn=(kaiser(M,B))';
hdn=hn.*wn;

[H,w]=freqz(hdn,[1],1000,'whole');
H=(H(1:501))';w=(w(1:501))';
mag=abs(H);
db=20*log10((mag)/max(mag));
subplot(2,2,1);
stem(n,hn,'r');title('原冲激响应')
subplot(2,2,2);
stem(n,wn,'g');title('窗口函数')
subplot(2,2,3);
stem(n,hdn,'b');title('改变后冲激响应')
subplot(2,2,4);
plot(fs*w/pi/2,db,'k');title('滤波器频谱')