I have fft of a signal, I want to calculate phase of that signal?

Sin(2*pi*f*t+phi)...i want phi from the fft of the given signal

Answer 1

[Star Strider]

Use the angle function. (You might also want the unwrap function.)

[Shrikant]

It gives the phase at every point...i just want the phase of the signal i.e. whether the signal has 90 or -90 phase.

[Star Strider]

The phase is by definition going to be the inverse sine of the value of your signal at t=0, or in a fft, the value (in radians or degrees) of the calculated phase compared to a similar signal with no phase. There appears to be no other way to calculate it.

Example:

t = linspace(0, 10*pi, 2500);
f = 5;
phi = pi/5;
s = [sin(2*pi*f*t);  sin(2*pi*f*t + phi)]';                         % Create Signals: s(:,1) phase - 0, s(:,2) phase = pi/5
Ts = mean(diff(t));
Fs = 1/Ts;
Fn = Fs/2;
fts = fft(s)/length(t);                                             % Do FFT
Fv = linspace(0, 1, fix(length(t)/2)+1)*Fn;
Iv = 1:length(Fv);

[pk,ix] = max(abs(fts(Iv,:)));
phsmin = [min(angle(fts(ix(1),:))); max(angle(fts(ix(2),:)))];
phsminpi = phsmin*pi;
phsdif = diff(phsmin);                                              % Calculate Phase Difference
out = sprintf('Phase difference = %.3f rad', phsdif)

figure(1)
subplot(2,1,1)
semilogy(Fv, abs(fts(Iv,:)))
grid
subplot(2,1,2)
plot(Fv, angle(fts(Iv,:)))
grid

[BA Mustafa]

t = 1 : 1000;

phaseshift= pi/5 ;

s1 = sin (2*pi*t/500);

s2 = sin (2*pi*t/500+ phaseshift);

Para1=s1;

Para2=s2;

time=t;

h1 = hilbert (Para1);

h2 = hilbert (Para2);

p1 = unwrap(angle(h1));

p2 = unwrap(angle(h2));

figure

plot (t,p1,t,p2);

title('evolution des phases des deux signaux','FontWeight','bold','FontSize',12)

xlabel('t (temps en secondes)','FontWeight','bold','FontSize',12);

ylabel('phase en radian','FontWeight','bold','FontSize',12);

legend('s1','s2');

grid on;

Depha_en_rad = mean (p2-p1)

Depha_en_degre = rad2deg(Depha_en_rad)