How can I plot the magnitude spectrum for these three filters?

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Faisal Alrafaei 2021-12-14

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回答： Ganesh 2024-6-12

%Low-pass Filter

B_lp = designfilt('lowpassfir', 'FilterOrder', 64, 'CutoffFrequency', 3e3, 'SampleRate', fs);

[b, a] = tf(B_lp);

x_lp = filter(B_lp, x);

%band-pass Filter

B_bp = designfilt('bandpassfir', 'FilterOrder', 64, 'CutoffFrequency1', 2000,'CutoffFrequency2', 5000, 'SampleRate', fs);

[b, a] = tf(B_bp);

x_bp = filter(B_bp, x);

%Low-pass Filter

B_hp = designfilt('highpassfir', 'FilterOrder', 64, 'CutoffFrequency', 4e3, 'SampleRate', fs);

[b, a] = tf(B_hp);

x_hp = filter(B_hp, x);

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Answer 1

Ganesh 2024-6-12

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Hi Faisal,

To plot the magnitude spectrum for the low-pass, band-pass, and high-pass filters you've designed, you can use MATLAB's "freqz" function, which computes and plots the frequency response of a filter. You may use the following documentation to learn more on the "freqz" function:

https://www.mathworks.com/help/signal/ref/freqz.html

The freqz function is used without specifying the number of points to use for the frequency response, which means the default setting is used for a detailed plot. The "fs" parameter is provided to scale the frequency axis according to your sampling frequency, allowing you to view the frequency response in Hz.

Note that this approach visualizes the filter characteristics themselves, not the spectrum of the filtered signal. If you're interested in the spectrum of the filtered signal (x_lp, x_bp, x_hp), you would need to use a different method, like performing a Fast Fourier Transform (FFT) on the filtered signals.