I tried using 'FFT' function in MATLAB to transform the given function from time to frequency domain...it gave me the graph but on the x axis the time domain(values) remained the same and did not change into frequency domain as the graph revealed..

I tried using 'FFT' function in MATLAB to transform the given function from time to frequency domain...it gave me the graph but on the x axis the time domain(values) remained the same and did not change into frequency domain as the graph revealed..

Answer 1

[Azzi Abdelmalek]

The fft function has one output argument, it's the discrete fourier transform of your function. you have to provide the frequency vector to plot your output.

[Hrushikesh]

can we use the FFT block in matlab simulink browser directly to calculate fourier transform....rather than programming in matlab and providing corresponding frequency values... if yes ...please tell me how?

[Azzi Abdelmalek]

Try Spectrum Analyzer from DSP System Toolbox

[Hrushikesh]

THANKS

Answer 2

[Walter Roberson]

How did you do the plotting? The fft() call does not do any plotting of its own, and if you call plot() then you need to pass in the correct x values for what the data represents.

[Hrushikesh]

i used the scope at the output of the fft block, which gave the plot of displacement vs time instead of disp. vs frequency...am i doin the right thing...?

Answer 3

[Aalya]

I am facing somehow a similar problem. However in my case, instead of having peak amplitude at the natural frequency, I am having it elsewhere. What could be wrong? I have obtained the time domain values from tout and simout parameters of simulink. My codes are below:

T=tout(2,1)-tout(1,1); %sample time

Fs=1/T; %sampling frequency

L=size(simout,1); %length of signal

t = (0:L-1)*T; % Time vector

y=simout(:,1);

figure(1)

plot(t,y)

title('time domain resonse of first mode')

xlabel('time (milliseconds)')

NFFT = 2^nextpow2(L); % Next power of 2 from length of y

Y = fft(y,NFFT)/L;

f = Fs/2*linspace(0,1,NFFT/2);

% Plot single-sided amplitude spectrum.

figure(2)

plot(f,2*abs(Y(1:NFFT/2)))

title('Single-Sided Amplitude Spectrum of y(t)')

xlabel('Frequency (Hz)')

ylabel('|Y(f)|')

Thanks