#Xf and spectrum code#

Second, for calculating fft in Matlab you can choose different resolutions, the Mathwork document and help use NFFT=2^nextpow2(length(signal)), it definitely isn't enough for one that wants high accuracy output.

#Xf and spectrum code#

This program calculates amplitude and phase spectra of an input signal with acceptable accuracy especially in the calculation of phase spectrum.The code does three main jobs for calculation amplitude and phase spectra.ДЇirst of all, it extends the input signal to infinity because for calculation Fourier transform(FT) (fft function in Matlab), we consider our signal is periodic with an infinite wavelength, the code creates a super_signal by putting original signal next to itself until the length of super_signal is around 1000000 samples, why did I choose 1000000 samples? Actually, it is just based on try and error!! For me, a supper signal with 1000000 samples has the best output. Look at this MATLAB function, it can calculate phase spectrum as well as amplitude spectrum with a perfect accuracy. The phase plot seems OK to me, especially after fftshift-ing it. from 0 Hz to 50 Hz.Д«y the way, if you plot plot(f,abs(Xf)/N), you will find that the peaks have an amplitude of 0.5A (being A the amplitude of the sinusoid). You could just plot the first half of your fft, i.e. It is true in this case, but it doesn't have to. Fs=100 %sampling frequencyДЇ=-Fs/2:Fs/N:Fs/2-Fs/N %frequency vectorД«) Assume the signal is real, so the spectrum is symmetric. This will take each frequency to its real place. There are two possible approaches here:ДЄ) Use fftshift to correct this issue. However, it isn't true that there is a peak in at 90Hz. Those peaks in your graph are consistent with this. You can do this theoretically, as shown in. The basic rule is: a sine of frequency f0 in time domain is a delta at f0 and -f0 in frequency. This is the most simple FT that you should understand.