firh.m

利用FIR滤波器设计一个低通滤波器

ws = 0.3*pi;          % 阻带截止频率
wp = 0.2*pi;
deltaw=ws-wp;
N0 = ceil(6.6*pi/ deltaw) + 1; %按哈明窗计算所需的滤波器阶数N0
N=N0+mod(N0+1,2);	  % 为了实现第一类偶对称滤波器，应使其长度N为奇数
n=0:N-1;
wdham =(hamming(N))';% 求窗函数
wc = (ws+wp)/2	;	% 截止频率取为两边界频率的平均值
hd = ideallp(wc,N);	% 求理想脉冲响应	
h = hd .* wdham;	% 设计的脉冲响应(即系数)为理想脉冲响应与窗函数乘积
[db,mag,pha,grd,w] = myfreqz(h,[1])	;% 对设计结果进行检验
dw = 2*pi/1000;
Rp = -(min(db(1:wp/dw+1)))        	% 检验通带波动
As = -round(max(db(ws/dw+1:501))) 	% 检验最小阻带衰减
subplot(2,2,1);stem(n,hd);title('IdealImpulseResponce');
axis([0,N-1,-0.1,0.3]);
xlabel('n');ylabel('hd(n)');
xa=0.*n;
hold on
plot(n,xa,'k');
hold off
subplot(2,2,2);stem(n,wdham);title('Hamming Window');
axis([0,N-1,0,1.1]);
xlabel('n');ylabel('w(n)');
subplot(2,2,3);stem(n,h);title('Actual Impulse Responce');
axis([0,N-1,-0,0.3]);
xlabel('n');ylabel('h(n)');
hold on
plot(n,xa,'k');
hold off
subplot(2,2,4);plot(w/pi,db);title('Magnitude Response in db');grid
axis([0,1,-100,10]);
xlabel('frequency in pi units');ylabel('decibles');
set(gca,'XTickMode','manual','XTick',[0,0.2,0.3,1]);
set(gca,'YTickMode','manual','YTick',[-30,0]);
set(gca,'YTickMode','manual','YTick',['30';0']);