fft - Octave (Matlab): Spectrum calculation -

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another question spectrum calculation in octave using fft:

with audacity created .wav file containing white noise, filtered lowpass fcut = 1khz, -20db/decade. spectrum analysed audacity looks expected (unfortunately can't post image since don't have enough reputation)

then analysed spectrum octave using following code:

  pkg load signal   %load signal package   graphics_toolkit ("gnuplot")  % use gnuplots    close   clear    [stereosig, fs,bit] =wavread('noise_stereo.wav'); % load wav   ch1 = stereosig(:,1); % left   ch2 = stereosig(:,2); % right    nfft = 1024;   nfft_half = nfft/2;   x = fft(ch1, nfft);   freqvect = (1:nfft_half+1)./nfft*fs;    figure(1)   x_mag_scaled = abs(x(1:nfft_half+1)./nfft_half);   semilogx(freqvect, 20*log10(x_mag_scaled));   grid on   xlabel('frequency (hz)')   ylabel('mag [db]')

the plot produced octave extremly "unsmooth", -20db/decade can not recognised since difference between 2 adjacent points can > 10db or so. 1khz cut off frequency can guessed.

does have idea how "smooth" spectrum done in audacity (which suppose reasonable solution)?

philippe


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