Having issues getting magnitude frequency response for a Difference equation

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Bernardo Rodriguez Jr
回答： nick 2023-11-23
I'm having trouble with an asignment (I started using Matlab a day ago) in which I need to get the magnitude of a difference equation as well as get the unit impulse response and store it in an array.
After some time looking online, and teaching myself how to do the z-transform, I managed to get this as my code:
% Difference equation -> y(n) = 0.2*x(n) + 0.34*x(n-10)
%Transform to z-plane -> H(z) = Y(z)/X(z) = 0.2 + 0.34z^-10
A = [0.2 0 0 0 0 0 0 0 0 0 0.34];
B = 1;
% Creates the transform function and plots magnitude/phase
H = filt(A,B);
figure;
bode(H);
% Plots unit impulse response
figure;
impulse(H);
The only probelm is that it isn't what my professor is looking for nor would he give an indication of what to do. I can't seem to find any documents online to help me with the problem, I'm not sure what it would fall under, however I think that I need to use the frequency response function? Any help would be much appreciated.
  1 个评论
Bernardo Rodriguez Jr
Bernardo Rodriguez Jr 2022-4-29
Update
I'm currently attempting this for the magnitude, but i'm still unsure if it is correct:
j = sqrt(-1);
w = linspace(-pi, pi);
H = 0.2 - 0.34*exp(-j*10*w);
figure;
stem(abs(H));

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回答（1 个）

nick
nick 2023-11-23
Hi Bernardo,
I understand from your query that you want to obtain the magnitude and impulse response of the difference equation.
I am assuming the given difference equation is a discrete time equation as you have used Z-transform. Thus, you are working with digital filters. You must use 'freqz' instead of 'bode' to obtain the frequency response, phase and magnitude, of digital filters. You may refer the following documentation of 'freqz' to learn more about it :
https://www.mathworks.com/help/signal/ref/freqz.html
Similarly, you must use 'impz' instead of 'impulse' to obtain impulse response of digital filters. You may refer the following documentation to learn more about 'impz':
https://www.mathworks.com/help/signal/ref/impz.html
Hope this helps,
Regards,
Neelanshu

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