Filter cutoff frequency correction
3 vues (au cours des 30 derniers jours)
Afficher commentaires plus anciens
Hello, I have this code to make a filter that cuts at 250 Hz and 0.7 amplitude, however, at 250 Hz I have 0.9441. Does anyone know how to correct this?
[b,a]=cheby1(3,0.5,2*pi*250,'s');
H=freqs(b,a,2*pi*[0:500]);
plot(0:500, abs(H))
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/722524/image.png)
0 commentaires
Réponse acceptée
Chunru
le 27 Août 2021
Modifié(e) : Chunru
le 28 Août 2021
% For digital filter
fs = 1000;
frp = 250; % freq at Rp
[b, a] = cheby1(3, 0.5, frp/(fs/2));
[h, f] = freqz(b, a, 2048, fs);
plot(f, abs(h));
hold on; grid on
% Get the 3db frequency
f3db = interp1(abs(h), f, sqrt(0.5));
% Iterative Correction
while abs(f3db-250)>0.1
frp = frp * (250/f3db);
[b, a] = cheby1(3, 0.5, frp/(fs/2));
[h, f] = freqz(b, a, 2048, fs);
f3db = interp1(abs(h), f, sqrt(0.5));
end
plot(f, abs(h));
plot(f3db, sqrt(0.5), 'o');
legend('Original', 'Corrected', '3dB');
% for analog filter
figure
fh = 250;
epsilon = sqrt(10.^(0.5/10)-1);
f0 = fh/cosh(1/3*acosh(1/epsilon));
[b,a]=cheby1(3,0.5,2*pi*f0,'s');
H=freqs(b,a,2*pi*[0:500]);
plot(0:500, abs(H));
hold on
xline(250)
grid on
4 commentaires
Plus de réponses (0)
Voir également
Catégories
En savoir plus sur Analog Filters dans Help Center et File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!