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I have a problem with butter filter and I can’t fix it
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Hello I just wrote this code and I have a problem with line which I used butter filter thank you
% Define the bandpass signal (sine wave)
fs = 1000; % sampling frequency
t = 0:1/fs:1-1/fs; % time vector
f1 = 100; % signal frequency
f2 = 300; % signal frequency
x = sin(2*pi*f1*t) + sin(2*pi*f2*t); % bandpass signal
% Obtain the Fourier transform of the bandpass signal
X = fft(x);
% Define the cutoff frequency for the lowpass filter
fc = 500; % cutoff frequency
% Create a Butterworth lowpass filter
N = 4; % filter orde
[b,a] = butter(N, fc/(fs/2));
% Apply the filter to the Fourier transform of the signal
Y = filter(b, a, X);
% Obtain the time-domain representation of the filtered signal
y = real(ifft(Y));
% Plot the original and filtered signals
figure;
subplot(2,1,1);
plot(t,x);
title('Bandpass Signal');
xlabel('Time (s)');
ylabel('Amplitude');
subplot(2,1,2);
plot(t,y);
title('Lowpass Filtered Signal');
xlabel('Time (s)');
ylabel('Amplitude');
0 个评论
采纳的回答
Les Beckham
2023-3-14
The error was because you were trying to set the cutoff frequency at the Nyquist frequency (half the sample rate).
The error message is pretty clear.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1324170/image.png)
Below is modified to format your code properly and adjust the cutoff frequency to a valid value. You can adjust to get the behavior you are looking for.
% Define the bandpass signal (sine wave)
fs = 1000; % sampling frequency
t = 0:1/fs:1-1/fs; % time vector
f1 = 100; % signal frequency
f2 = 300; % signal frequency
x = sin(2*pi*f1*t) + sin(2*pi*f2*t); % bandpass signal
% Obtain the Fourier transform of the bandpass signal
X = fft(x);
% Define the cutoff frequency for the lowpass filter
fc = 400; %500; % cutoff frequency <<< You can't set a cutoff at the Nyquist frequency (half the sample rate)
% Create a Butterworth lowpass filter
N = 4; % filter order
fc/(fs/2) % <<< valid (less than 1)
[b,a] = butter(N, fc/(fs/2));
% Apply the filter to the Fourier transform of the signal
Y = filter(b, a, X);
% Obtain the time-domain representation of the filtered signal
y = real(ifft(Y));
% Plot the original and filtered signals
figure;
subplot(2,1,1);
plot(t,x);
title('Bandpass Signal');
xlabel('Time (s)');
ylabel('Amplitude');
subplot(2,1,2);
plot(t,y);
title('Lowpass Filtered Signal');
xlabel('Time (s)');
ylabel('Amplitude');
3 个评论
Rik
2023-3-14
Next time, please format the code as code yourself.
If this answer solved your question, please consider marking it as accepted answer and/or giving it an upvote.
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