3Â¥: Originally posted by sudo at 2011-07-25 20:44:28
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[P,F]=periodogram(x, window, nfft, Fs)

ty = y(1:5:end); %½«Ô­À´2000HzµÄÊý¾Ý½µ²ÉÑùµ½400Hz
ty = ty - mean(ty); %¼õÈ¥Ö±Á÷·ÖÁ¿
[P,F]=periodogram(ty,[],[],400); %Çó¹¦ÂÊÆ×
plot(F, P) %»­Í¼

function [P,f]=fftpsd(x,Fs)
    m = length(x);          % Õû¸öÊý¾Ý³¤¶È
    n = pow2(nextpow2(m));  % À©Õ¹µ½ºÏÊʳ¤¶È£¬2µÄÕûÊý´ÎÃÝ
    y = fft(x,n);           
    f = (0:n-1)*(Fs/n);     %ƵÂÊ·¶Î§
    P = y.*conj(y)/n;   %¹¦ÂÊÆ×ÃܶÈ

    f=f(1:n/2);
    P=P(1:n/2);
   
    %plot(f,10*log10(P)); %°ÑÊý¾Ýת»»ÎªdB
    plot(f,P);
    grid;
    xlabel('Frequency (Hz)');
    ylabel('Power(dB)');
    title('{\bf Periodogram}');