[Scilab-users] ?==?utf-8?q? shift phase in fft

[Antoine Monmayrant]

Hi Paul,

What are you trying to achieve exactly?
If you apply a phase shift, you actually just multiple your signal by exp(i*phi), both in the time and frequency domain.
Not much to see actually.

Now, if you apply a linear a phase shift in time  ie S1(t)->S1(t)*exp(i*Omega*t), this will result in a spectral shift: S1fft(nu)->S1fft(nu+/-Omega/2Pi).

Hope it helps,

Antoine
 
Le Jeudi, Septembre 29, 2016 12:29 CEST, paul.carrico at free.fr a écrit: 
 
> Dear all 
> 
> 
> I'm sorry about asking a so basic question, but I do not understand how to make a shift phase in a fft ; There's something I do not catch what ? 
> 
> 
> Regards 
> 
> 
> Paul 
> 
> 
> 
> 
> ###################################################### 
> 
> mode(0) 
> clear all 
> 
> 
> f = 10; // frequency 
> omega = 2*%pi*f; // circular frequency 
> nb_T = 5; // number of periods 
> t1 = 0; 
> t2 = (nb_T / f); 
> n = 10; 
> t = linspace(t1,t2,2^n)'; // must be a power of 2 
> nl = size(t,"*"); 
> 
> 
> s1 = 2*sin(omega*t); // original signal 
> plot(t,s1,"r"); 
> 
> 
> phi = %pi/3; 
> s2 = 2*sin(omega*t + phi); // targetted signal to be rebuilt 
> plot(t,s2,"b"); 
> 
> 
> // shift phase in the fft 
> s1_fft = fft(s1); 
> s1_fft = clean(s1_fft); 
> 
> //s1_fft = s1_fft. * exp(-%i*phi/nl); 
> s1_fft = s1_fft. * exp(-%i*phi); 
> s1_new = ifft(s1_fft); 
> plot(t,s1_new,"g"); 
> 
>