fg_04_19.m

来自「英文书《Digital Signal Processing with Examp」· M 代码 · 共 22 行

% fg_04_19
% Chapter 4, fig. 4.19. Four filter types.
sp_fig(1,9,6);
f=[.15 0 0 0; 0 .35 .4 .45; .1 .15 .3 .4; .15 .2 .25 .3];
dBs=40;
ifilt=str2mat('Lowpass','Highpass','Bandpass','Bandstop');
for i=1:4,
   [b,a]=spiird(3,i,6,f(i,1),f(i,2),f(i,3),f(i,4),dBs);
   nu=linspace(0,.5,500);
   pwr=abs(gain_f(b,a,nu)).^2;
   dB=10*log10(max(pwr,10^(-dBs/10)));
   subplot(2,2,i);
   plot(nu,dB,'k'); grid;
   axis([0 .5 -40 10]);
   set(gca,'fontname','times','fontsize',16);
	if i>2,
	   xlabel('Frequency (Hz-s)');
	end
   ylabel('Power gain (dB)');
   text(.15,5,ifilt(i,:),'fontname','times','fontsize',16);
end