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How can i determine phase in FFT?

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Big dream
Big dream on 24 Oct 2016
Commented: Star Strider on 1 Jun 2018
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.

Accepted Answer

Star Strider
Star Strider on 24 Oct 2016
Edited: Star Strider on 24 Oct 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.
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More Answers (1)

karinkan
karinkan on 1 Jun 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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