% Design example comparing various FIR windows for
% same length filter
% 
% Here we have a lowpass filter with a cutoff frequency of 100 Hz
% The sampling frequency is 1000 Hz and a transition width of 75 Hz
%
% The Blackman window needs the most coefficients so we will compute
% the length of the filter for it and compare all others to it.
% 
% Normalized transition width is (75 Hz/1000 Hz) = 0.075
% The length of the filter is then N = 5.5/(0.075) = 73.
FS = 1000;
FN = 500;
N = 73;
FC = 100/FN;
hn = fir1(N-1, FC, boxcar(N));
[H,f] = freqz(hn, 1, 512, FS);          % Compute frequency response
mag = 20*log10(abs(H));
subplot(3,2,1), plot (f, mag), grid on
xlabel ('Frequency (Hz)')
ylabel ('Magnitude Response (dB)')
title ('Rectangular Window')
hn = fir1(N-1, FC, bartlett(N));
[H,f] = freqz(hn, 1, 512, FS);          % Compute frequency response
mag = 20*log10(abs(H));
subplot(3,2,2), plot (f, mag), grid on
xlabel ('Frequency (Hz)')
ylabel ('Magnitude Response (dB)')
title ('Bartlett Window')
hn = fir1(N-1, FC, hamming(N));
[H,f] = freqz(hn, 1, 512, FS);          % Compute frequency response
mag = 20*log10(abs(H));
subplot(3,2,3), plot (f, mag), grid on
xlabel ('Frequency (Hz)')
ylabel ('Magnitude Response (dB)')
title ('Hamming Window')
hn = fir1(N-1, FC, hann(N));
[H,f] = freqz(hn, 1, 512, FS);          % Compute frequency response
mag = 20*log10(abs(H));
subplot(3,2,4), plot (f, mag), grid on
xlabel ('Frequency (Hz)')
ylabel ('Magnitude Response (dB)')
title ('Hanning Window')
hn = fir1(N-1, FC, blackman(N));
[H,f] = freqz(hn, 1, 512, FS);          % Compute frequency response
mag = 20*log10(abs(H));
subplot(3,2,5), plot (f, mag), grid on
xlabel ('Frequency (Hz)')
ylabel ('Magnitude Response (dB)')
title ('Blackman Window')