FIR-Filter designing Matlab code
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Fs=8000; %Specify Sampling Frequency
Ts=1/Fs; %Sampling period.
Ns=512; %Nr of time samples to be plotted.
t=[0:Ts:Ts*(Ns-1)]; %Make time array that contains Ns elements
%t = [0, Ts, 2Ts, 3Ts,..., (Ns-1)Ts]
f1=500;
f2=1500;
f3=2000;
f4=3000;
x1=sin(2*pi*f1*t); %create sampled sinusoids at different frequencies
x2=sin(2*pi*f2*t);
x3=sin(2*pi*f3*t);
x4=sin(2*pi*f4*t);
x=x1+x2+x3+x4; %Calculate samples for a 4-tone input signal
%N=16; %FIR1 requires filter order (N) to be EVEN
%when gain = 1 at Fs/2.
%W=[0.4 0.6]; %Specify Bandstop filter with stop band between
%0.4*(Fs/2) and 0.6*(Fs/2)
%B=FIR1(N,W,'DC-1'); %Design FIR Filter
disp('Please specify the filter type');
FilterType={'low','high','bandpass','stop'};
disp('Here is the filter option:');
disp('1: Low Pass Filter ');
disp('2: High Pass Filter');
disp('3: Band Pass Filter');
disp('4: Band Stop Filter');
disp('You only need enter number. EX. 4 means Band Stop filter')
FilterOption=input('FilterOption=');
while FilterOption ~=1 && FilterOption ~=2 && FilterOption ~=3 && FilterOption ~=4
disp('You only need enter number : 1,2,3 or 4. EX. 4 means Band Stop filter');
FilterOption=input('FilterOption=');
end
userFilterType=FilterType{FilterOption};
disp('Enter the order of the filter(Must be a positive even number, should be less than 100');
FilterOrder=input('FilterOrder=');
str=sprintf('Here is all the frequency infromation in this experiment:Fs=%d; f1=%d; f2=%d; f3=%d; f4=%d;',Fs,f1,f2,f3,f4);
disp(str);
if FilterOption==1
disp('Enter the Edge Freq. in Hz. Note: the value should be within 0~Fs');W=input('omega=');
elseif FilterOption==2
disp('Enter the Edge Freq. in Hz. Note: the value should be within 0~Fs');W=input('omega=');
elseif FilterOption==3
disp('Enter the Edge Freq. in Hz. Note: the value should be within 0~Fs');W=input('omega cutoff1=');W2=input('omega cutoff2='); W=[W W2];
elseif FilterOption==4
disp('Enter the Edge Freq. in Hz. Note: the value should be within 0~Fs');W=input('omega cutoff1=');W2=input('omega cutoff2='); W=[W W2];
end
%Fs, W,
W=W./(Fs/2); % [1600 2400]
N=FilterOrder;
Window_Option={'hamming','rectwin'};
disp('Here is the Windowing option:');
disp('1: hamming');
disp('2: rectwin');
WindowOption=input('WindowOption=');
while WindowOption ~=1 && WindowOption ~=2
disp('You only need enter number : 1 or 2 means rectwin');
WindowOption=input('WindowOption=');
end
%WindowOption='rectwin';
switch Window_Option{WindowOption}
case 'hamming'
userWindow=hamming(N+1);
case 'rectwin'
userWindow=rectwin(N+1);
otherwise
disp('Wrong windowing option. EXIT');
eixt
end
%B=FIR1(N,W,'bandpass',userWindow); %Design FIR Filter
B=fir1(N,W,userFilterType,userWindow); %Design FIR Filter
%B %Leaving off semi-colon causes contents of
%B (the FIR coefficients) to be displayed.
A=1; %FIR filters have no poles, only zeros.
figure;
zerophase(B,A);
disp('Checking the Zero-Phase Response of the designed filter, enter any key to continue');
pause;
figure; %Create a new figure window, so previous one isn't lost.
freqz(B,A); %Plot frequency response - both amp and phase response.
disp('Checking the Freq. Response of the designed filter, enter any key to continue');
pause;
figure;
subplot(2,1,1); %Two subplots will go on this figure window.
Npts=200;
plot(t(1:Npts),x(1:Npts)) %Plot first Npts of this 4-tone input signal
title('Time Plots of Input and Output');
xlabel('time (s)');
ylabel('Input Sig');
%Now apply this filter to our 4-tone test sequence
y = filter(B,A,x);
subplot(2,1,2); %Now go to bottom subplot.
plot(t(1:Npts),y(1:Npts)); %Plot first Npts of filtered signal.
xlabel('time (s)');
ylabel('Filtered Sig');
disp('Checking the Filtering Effect of the designed filter in time domain, enter any key to continue');
pause;
figure; %Create a new figure window, so previous one isn't lost.
subplot(2,1,1);
xfftmag=(abs(fft(x,Ns))); %Compute spectrum of input signal.
xfftmagh=xfftmag(1:length(xfftmag)/2);
f=[1:1:length(xfftmagh)]*Fs/Ns; %Make freq array that varies from
%0 Hz to Fs/2 Hz.
plot(f,xfftmagh); %Plot frequency spectrum of input signal
title('Input and Output Spectra');
xlabel('freq (Hz)');
ylabel('Input Spectrum');
subplot(2,1,2);
yfftmag=(abs(fft(y,Ns)));
yfftmagh=yfftmag(1:length(yfftmag)/2);
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