MATLAB Program for FIR Filter Using Window

Popular window coefficients.

1. hann() - for hanning window
2. hamming() - for hamming window
3. blackman() - for blackman window
4. kaiser() - for kaiser window

% Program to design a FIR filter using windows.

close all;

clear all;

fp=input('Enter the pass band frequency');

fs=input('Enter the stop band frequency');

rp=input(' Enter the pass band attenuation');

rs=input('Enter the stop band attenuation');

f=input(' Enter the sampling frequency');

%Calculating filter order

num=-20*log10(sqrt(rp*rs))-13;

dem=14.6*(fs-fp)/f;

n=ceil(num/dem);

n=abs(n);

% Normalizing the frequencies

wp=2*fp/f;

ws=2*fs/f;

wn=(ws+wp)/2;

%Adjusting the filter order. The order of window must be an odd number 

%and the order of filter must be one less than that of the window 

if (rem(n,2)==0)

    m=n+1;

else

        m=n;

        n=n-1;

end

%Window sequence calculation

w=hann(m);

%Calculation of filter coefficients

b=fir1(n,wn,'low',w);

%Plotting the filter response

freqz(b,1,500,3000);

TITLE('Magnitude and Phase response');

Output:

%output

%Enter the pass band frequency1000

%Enter the stop band frequency1200

%Enter the pass band attenuation.2

%Enter the stop band attenuation45

%Enter the sampling frequency3000

You can change this lowpass filter to high pass filter by changing the option 'low' to 

'high' in the fir1() function. The output is shown below.

%output

%Enter the pass band frequency1200

%Enter the stop band frequency1000

%Enter the pass band attenuation.2

%Enter the stop band attenuation45

%Enter the sampling frequency3000