How can i plot the magnitude and phase response my output signal?

Hi,

How can I plot the magnitude and phase response of y[n] that i have obtained? y[n] = [-3 8 5 2]

I have followed this but my magnitude graph looks weird. (a V continuous line)

Here's my code:

Trial>> t = 0:1/100:10-1/100;  
Trial>> x = [-3 8 5 2]
Trial>> y = fft(x);
Trial>> m = abs(y);
Trial>> f = (0:length(y)-1)*100/length(y); 
Trial>> subplot(2,1,1)
Trial>> plot(f,m)
Trial>> title('Magnitude')

Thank you

[Aditya Desai]

What is x here? If it is the signal, then should it not be the same size as t?

[DJrocker]

x is the discrete signal values y[n]. What is t?

[Geoff Hayes]

t is the array of sample times which is the first variable that you define above (but never use thereafter). Why does your x only have four samples?

Answer 1

[Star Strider]

The correct code for the Bode plot for your signal:

t = linspace(0,10,4);
Ts = mean(diff(t));                                     % Sampling Interval
Fs = 1/Ts;                                              % Sampling Frequency
Fn = Fs/2;                                              % Nyquist Frequency
x = [-3 8 5 2];
y = fft(x);
m = 2*abs(y)/length(x);
f = linspace(0, 1, fix(length(y)/2)+1)*Fn;
Iv = 1:length(f);                                       % Index Vector
subplot(2,1,1)
plot(f,m(Iv))
title('Magnitude')
subplot(2,1,2)
plot(f,angle(y(Iv)))
title('Phase')
xlabel('Frequency')