How can i determine phase in FFT?
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Big dream
el 24 de Oct. de 2016
Comentada: Star Strider
el 28 de Jun. de 2023
Hi everyone, right now im trying to calculate signal phases using angle(x) from FFT Function im Matlab. Noted that i've coded the program like below :
%%Plotting Grafik
%create a time vector 't', containing integers from 1 to n(summary of data)
count= length(data);
Ts=mean(diff(times1));
Fs=1/Ts;
NFFT=2^nextpow2(count);
y=fft(data,NFFT)/count;
f=Fs/2*linspace(0,1,NFFT/2+1);
figure(2)
plot(f,2*abs(y(1:NFFT/2+1)));
grid on
title('Single-Sided Amplitude Spectrum of y(t)');
xlabel('Frequency(Hz)');
ylabel('|Y(f)|');
phase=angle(y);
But i'm not really sure with the phase function. Does anyone ever has the same experience?
Thanks before for your answer.
6 comentarios
WH Wang
el 28 de Jun. de 2023
it's atan2(imaginary,real) in matlab, or using phase() function of matlab.
Star Strider
el 28 de Jun. de 2023
There is no phase function that I can find in the documentation, however there is the angle function that returns the phase angle (in radians) of a complex argument.
Respuesta aceptada
Star Strider
el 24 de Oct. de 2016
Editada: Star Strider
el 24 de Oct. de 2016
Your code appears to me to be correct, including the ‘phase’ assignment. Note that the units of ‘phase’ are in radians. Convert them to degrees (if desired) by multiplying them by 180/pi.
I’m not certain what you want, so also consider the unwrap function. Use it on the radian units, and convert to degrees later if necessary.
EDIT — If you want to plot it, the easiest way is to use the subplot function. Your plotting code changes to:
phase=angle(y);
figure(2)
subplot(2,1,1)
plot(f,2*abs(y(1:NFFT/2+1)));
grid on
title('Single-Sided Spectrum of y(t)');
ylabel('|Y(f)|');
subplot(2,1,2)
plot(f,phase)
grid on
xlabel('Frequency(Hz)');
ylabel('Phase (rad)')
I did not test that, but it should work.
14 comentarios
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karinkan
el 1 de Jun. de 2018
I am a bit confusing that the following two equations which one is correct? eq.1 y=fft(data,NFFT)/count; eq.2 y=fft(data,NFFT)/NFFT;
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