Hi, I am trying to plot my signal(sum of two sines of different frequencies) in the the frequency domain using FFT function of matlab. The magnitude plot -> y_mag = real(fft(x,N) is giving correct result. But the phase plot -> y_phase = imag(fft(x,N)); is not giving correct result..... Can someone help me..? Thanks & Regards, shakes_ck _____________________________________ Do you know a company who employs DSP engineers? Is it already listed at http://dsprelated.com/employers.php ?

# Matlab FFT function does not give the correct result

Started by ●May 16, 2007

Posted by ●May 16, 2007

On 16 mai, 12:38, "shakes_ck" <chandrasheka...@patni.com> wrote:> Hi,Hi,> I am trying to plot my signal(sum of two sines of different frequencies) > in the the frequency domain using FFT function of matlab. > The magnitude plot -> y_mag = real(fft(x,N) > is giving correct result. > But the phase plot -> y_phase = imag(fft(x,N)); > is not giving correct result..... > Can someone help me..?You make an error when you resp. compute the magnitude and the phase of your fft using the real and imaginary part of it. To obtain the magnitude plot, you should use the modulus of your Fourier signal: y_mag = abs(ff((x,N)); For the phase plot, you should use the function angle: y_phase angle(fft(x,N)); or the unwrapped phase using the matlab function unwrap: y_phase unwrap(angle(fft(x,N)));> > Thanks & Regards, > shakes_ck >Matthieu

Posted by ●May 16, 2007

shakes_ck wrote:> Hi, > I am trying to plot my signal(sum of two sines of different frequencies) > in the the frequency domain using FFT function of matlab. > The magnitude plot -> y_mag = real(fft(x,N) > is giving correct result. > But the phase plot -> y_phase = imag(fft(x,N)); > is not giving correct result..... > Can someone help me..?Are you accounting for phase wrapping? Jerry -- Engineering is the art of making what you want from things you can get. Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯

Posted by ●May 16, 2007

shakes_ck wrote:> Hi, > I am trying to plot my signal(sum of two sines of different frequencies) > in the the frequency domain using FFT function of matlab. > The magnitude plot -> y_mag = real(fft(x,N) > is giving correct result. > But the phase plot -> y_phase = imag(fft(x,N)); > is not giving correct result..... > Can someone help me..?Are you accounting for phase wrapping? Jerry -- Engineering is the art of making what you want from things you can get. Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯Â¯

Posted by ●May 16, 2007

On 16 mai, 12:38, "shakes_ck" <chandrasheka...@patni.com> wrote:> Hi,Hi,> I am trying to plot my signal(sum of two sines of different frequencies) > in the the frequency domain using FFT function of matlab. > The magnitude plot -> y_mag = real(fft(x,N) > is giving correct result. > But the phase plot -> y_phase = imag(fft(x,N)); > is not giving correct result..... > Can someone help me..?You make an error when you resp. compute the magnitude and the phase of your fft using the real and imaginary part of it. To obtain the magnitude plot, you should use the modulus of your Fourier signal: y_mag = abs(ff((x,N)); For the phase plot, you should use the function angle: y_phase angle(fft(x,N)); or the unwrapped phase using the matlab function unwrap: y_phase unwrap(angle(fft(x,N)));> > Thanks & Regards, > shakes_ck >Matthieu

Posted by ●May 16, 2007

Hi, I am trying to plot my signal(sum of two sines of different frequencies) in the the frequency domain using FFT function of matlab. The magnitude plot -> y_mag = real(fft(x,N) is giving correct result. But the phase plot -> y_phase = imag(fft(x,N)); is not giving correct result..... Can someone help me..? Thanks & Regards, shakes_ck _____________________________________ Do you know a company who employs DSP engineers? Is it already listed at http://dsprelated.com/employers.php ?