fir_iir.m

关于Digital Signal Process中FIR

%Create a signal
t = [0:0.001:1];
t_display = 100;
signal=cos(2*pi*50*t);
figure;
subplot(2,4,1);
plot(t(1:t_display),signal(1:t_display)),title('ORIGINAL SIGNAL(T-DOMAIN)'),xlabel('time (s)');

%Add noise to the signal
randn('state',0);
sign_and_noise = signal + 0.5*randn(size(t));
hold on;subplot(2,4,2);
plot(t(1:t_display),sign_and_noise(1:t_display)), title('NOISE SIGNAL(T-DOMAIN)');xlabel('time (s)');


%Transfer the original signal to frequency domain
SIG= fft(signal);
subplot(2,4,5);
plot([1:1001],SIG(1:1001)),title('ORIGINAL SIGNAL(F-DOMAIN)');
ylabel('magnitude');

%Transfer the noise signal to frequency domain
SIG_NOISE= fft(sign_and_noise);
subplot(2,4,6);
plot([1:1001],SIG_NOISE(1:1001)),title('NOISE SIGNAL(F-DOMAIN)');
ylabel('magnitude');


%Create a low pass filter
length=1001;
cutoff=70;
filter=[ones(1,cutoff) zeros(1,(length-cutoff))];
subplot(2,4,7);
plot([1:length], filter),title('FILTER (F-DOMAIN)');
ylabel('magnitude');

%transfer the filter to time domain
subplot(2,4,3);
plot(t,fftshift(real(ifft(filter)))),title('FILTER (T-DOMAIN)'),xlabel('time (s)');



%Product in frequency domain
res1 = SIG_NOISE .* (filter);
res1= real(ifft(res1));
res1 =fftshift(res1);
subplot(2,4,8);
plot(t(1:t_display), res1(1:t_display),'r'),title('Result from Frequence filter');xlabel('time (s)');

%Convolution in time domain
res2 = conv(sign_and_noise, real(ifft(filter)));
subplot(2,4,4);
plot(t(1:t_display), res2(1:t_display),'r'),title('Result from Convolution');xlabel('time(s)');