how to design a FIR filter.

 DESING OF FIR FILTER WITH BOTH HAMMING AND BLACKMAN WINDOW METHOD

Answer 1

[Emanuel]

Hello Paul,

I think it can help you!

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function [b,a] =  my_fir_emanuel(Ap,As,fc,fs,Fs)

close all

%This routine will be used to obtain the coefficient of a FIR filter. 
%After entering the required parameters the type of filter (low pass, 
%high pass, band-pass or band-stop) and the window function is 
%automatically selected.

%For details on FIR filter specifications recommended reading the book
% E.C. Ifeachor, Digital Signal Processing - A Pratical Approach,
%Pearson Education, 2ª Edition, 2002.

%Especificações do Filtro FIR (FIR Filter Specifications
)

% fc = [fc1 fc2] 

% fs = [fs1 fs1]

% Ap [1x1]

% As [1x1]
% Fs [1x1]

%Obs.: fc2 e fs2 apenas para filtros passa-faixa ou rejeita-faixa
Note: fc2 and fs2 only for band-pass filters or band-stop.

%Frequencia normalizada(Normalized Frequency)

fcn = fc/Fs;

fsn = fs/Fs;

f0n = 1000/Fs;

%Faixa de transição(Transition range)

df= abs(fc(1)-fs(1));

dfn= df/Fs;

%Seleciona a  função janela (select de window function)
%
if As<=21 && Ap>=0.7416

N=ceil(0.9/dfn); 

w=rectwin(N);%Função ajanelamento(Window Function)
disp('Rectangular Window Chosen')

elseif As<=44 && Ap>=0.0546

N=ceil(3.1/dfn) %a função ceil aredonda os coeficientes para mais ex: 3.2 aredonda para 4

w = hanning(N);%Função de Ajanelamento

   disp('Hanning window chosen')

elseif As<=53 && Ap>=0.0194

      N=ceil(3.3/dfn)

      w = hamming(N);%Função de Ajanelamento 

      disp('Hamming window chosen')

elseif As<=75 && Ap>=0.0017

          N=ceil(5.5/dfn)

          w = blackman(N);%Função de Ajanelamento 

              disp('Blackman window chosen')

elseif As<90 && Ap>=0.000275

              N=ceil(4.71/dfn)

              w = kaiser(N);%Função de Ajanelamento 
                 disp('Kaiser window chosen')

end

n= 1: (N-1)/2;

% Função resposta ao impulso ideal

% Selects the filter type

%Low-Pass Filter

if  fc(1)<fs(1)&& length(fc)==1

hi0= 2*fcn(1);

hip = (2*fcn(1)*sin(2*pi*fcn(1)*n)./(2*pi*fcn(1)*n));

hin = fliplr(hip);

hi = [hin hi0 hip];

stem(hi)

disp('Low-Pass Filter selected')

%High-Pass Filter

elseif  fc(1)>fs(1) && length(fc)==1

      if length(fc)==2

hi0= 1-2*fcn(1);

hip = (-2*fcn(1)*sin(2*pi*fcn(1)*n)./(2*pi*fcn(1)*n));

hin = fliplr(hip);

hi = [hin hi0 hip];

stem(hi)

disp('High-Pass Filter Selected')
    end
%Band-Stop Filter

elseif (length(fc)==2) && (length(fs)==2)

      if fc(1)<fs(1)&& fc(2)>fs(2) && (length(fc)==2)

hi0= 1-2*(fcn(2)-fcn(1));

hip = (2*fcn(1)*sin(2*pi*fcn(1)*n)./(2*pi*fcn(1)*n))-(2*fcn(2)*sin(2*pi*fcn(2)*n)./(2*pi*fcn(2)*n));

hin = fliplr(hip);

hi = [hin hi0 hip];

stem(hi)

disp('Band-Stop Filter Selected')

      end

%Band-Pass Filter
elseif (length(fc)==2) && (length(fs)==2)

      if fc(1)>fs(1)&& fc(2)<fs(2) %&&

hi0= 2*(fcn(2)-fcn(1));

hip = (2*fcn(2)*sin(2*pi*fcn(2)*n)./(2*pi*fcn(2)*n))-(2*fcn(1)*sin(2*pi*fcn(1)*n)./(2*pi*fcn(1)*n));

hin = fliplr(hip);

hi = [hin hi0 hip];

stem(hi)
disp('Band-Pass Filter Selected')

      end

disp(' ')

disp(' ')

elseif  fc(1)>fs(1)& fc(2)> fs(2)

error('Impossível selecionar o tipo de filtro com os dados de entrada fc e fs.Digite: Help my_fir_emanuel para instruções')

elseif  fc(1)==0 & fc(2)==1

error('Unable to select filters with the input data')

elseif  fs(1)==0 & fs(2)==1

error('Unable to select filters with the input data')

end

%if size(hi,1)

% Desired impulse response function

if length(hi) == length(w)

      b = hi.*w';
  a=1;

figure(1)

stem(b)

figure(2)

freqz(b,a,1000,Fs);

%error('Impossível determinar a resposta em frequência para os parâmetros escolhidos')    

end

Answer 2

[Wayne King]

You can use fdesign

You do not give any information about your filter. Here is a lowpass filter with a cutoff frequency of 0.2 radians/sample and an order of 20.

d = fdesign.lowpass('N,Fc',20,0.2);
Hd1 = window(d,'window',@hamming);
Hd2 = window(d,'window',@blackman);

[AJAY KUMAR]

how to design without using rectwin function....