How to Plot fft of ascii values in MATLAB? -

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i have ascii file containing 2048 x , y value pairs. want know how plot fft of y in matlab. writing following matlab code not able find appropriate result.

how can this? have tried:

i = load('data1.asc');  = 1:2048     y = i(:,2); end  plot(x)  fs = 40000;                     t = 1/fs;                    l = 2000;      nfft = 2^nextpow2(l); y = abs(fft(y,nfft))/l; f = fs/2*linspace(0,1,nfft/2+1);  figure, plot(f,2*abs(y(1:nfft/2+1)))  axis([0 40000 0 40]) xlabel('frequency (hz)') ylabel('|y(f)|')

instead of diving straight matlab's fft routine should instead consider using periodogram function. when people "fft" usual mean psd or periodogram, i.e. plot of power spectral density using suitably windowed , ffted sample. periodogram function in matlab takes care of details of you, i.e. applying window function, calculating fft, deriving magnitude fft output, appropriate scaling of axes, , plotting if required.

note: periodogram in matlab signal processing toolbox - if not have access can either consider using octave (free matlab clone) has periodogram clone, otherwise need put various building blocks yourself:

  • window function
  • fft
  • calculate magnitude
  • take scare of scaling of freq , magnitude values
  • plot psd

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