Low pass filter VS high pass filter
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Omar Abulayla
le 21 Jan 2021
Réponse apportée : Star Strider
le 21 Jan 2021
I have this filter and I want to analyze it. How can I know from the plot that its a highpass filter or a lowpass filter?
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Star Strider
le 21 Jan 2021
Calculate the Fourier transform of the filter from the signals.
t = ...; % Time Vector
s = ...; % Original Signal Vector
s_filtered = ...; % Filtered Signal Vector
Ts = mean(diff(t)); % Sampling Interval (Assumes Constant Intervals)
Fs = 1/Ts; % Sampling Frequency
Fn = Fs/2; % Nyquist Frequency
L = numel(t); % Signal Length
FTs = fft(s)/L % Fourier Transform of Original Signal
FTs_filt = fft(s_filtered)/L; % Fourier Transform of Filtered Signal
Fv = linspace(0, 1, fix(L/2)+1)*Fn; % Frequency Vector (One-Sided Fourier Transform)
Iv = 1:numel(Fv); % Index Vector (One-Sided Fourier Transform)
H = FTs_filt ./ FTs; % Complex Transfer Function
figure
subplot(2,1,1)
plot(Fv, abs(H(Iv)))
ylabel('Amplitude')
grid
subplot(2,1,2)
plot(Fv, angle(H(Iv)))
xlabel('Frequency')
ylabel('Phase')
grid
sgtitle('Bode Plot of Filter')
That should reveal the filter characteristics, as well as reasonably accurate aspects of its design (e.g. passband and stopband frequencies).
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Mathieu NOE
le 21 Jan 2021
hello
you can do a bode plot of the transfer function between the output (signal filtered) vs the input (raw signal)
use tfestimate for transfer function estimation from time data and you will be able to fit a filter TF to that
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