I have a signal,
fs = 100; % Sample frequency (Hz) t = 0:1/fs:10-1/fs; % 10 sec sample x = (1.3)*sin(2*pi*15*t) % 15 Hz component + (1.7)*sin(2*pi*40*(t-2)) ; % 40 Hz component
when I take fft of x then its amplitude and phase spectrum are:
And now if deliberately I will put the leading 10 values to zeros
x(1:10) = 0;
then as per my understanding the frequency of the complete data set is not changed so the fft would not be changed. Which is supported by the amplitude fft response.
But the phase plot is showing some strange result.
Can some help me why the response is changed. Although they both are following the same equation. Also If I have a equation cos(2*pift) and my t is from 3:Tp and before time =3sec the response is zero, then will it not have the same response as t:0:Tp.