FFT - Return vector and Frequency display

fft function - it returns a vector, same length as the signal, but if we plot the abs(signalFFT), the x axis does not quite depict the exact frequency, although it is very close. I would want to know how does this fft function works, what it exacts returns & how and what do I do to fix this.

Answer 1

[kholoud salameh]

hi , if you try this code :

f = abs(fft(y));

plot(f)

it will plot y by sample at x-axis which is the length of f ! to get y by the exact frequency try this one :

f = abs(fft(y)); % calculate the magnitude of fft

index = 1:length(f);

index = index ./length(f) ;

index = index * fs ;

figure

plot(index,f); % plot frequency spectrum