FFT() Application for a real sound data

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TESFAW 2014-8-10

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https://ww2.mathworks.cn/matlabcentral/answers/147041-fft-application-for-a-real-sound-data

编辑： TESFAW 2014-8-22

    He! everybody
      I am Tesfaw
   I am confused to do my project on signal processing and I need help fro the 
    forum.The project is to determine the fundamental frequency of a Toyota 
     engine sound(idle) using user defined codes. My attempt is below.
    Ns=samples=131072; 
    Fs=44100; %sampling frequency
    %channel 1 ,data type double in .wav format
    [z,Fs]=wavread('normal.wav',131072);
     N=length(z);%length of the recorded sound 
     %conversion to binary
     b=bin2dec(fliplr(dec2bin(0:N-1)))+1;
    %make it bit reversed order
     MC=y(b);
     s=which('normal.wav');
     set(gcf,'color',get  
(0,'DefaultUIcontrolBackgroundColor'),'NumberTitle','off','Name',s,'Resize','on','Menubar','none');
    %calculate the frequency
    fr = (0:(N/128)-1)*Fs/N;
    p = abs(MC(1:N/128));
    [Amax,f] = max(p);
    fprintf('Max.Magn. of Amp1. is %6.4f db/n and the freq f is %
     4.2f\n',Amax,f);
    pp=fftshift(p);
   %plot the figure
    plot(fr,pp,'b') 
    I need to determine the Amax(maximum amplitude) and the frequency 
       at which Amax occur
      but the result from  plot and from fprintf code is not the same
      Please corret me 
      I am thankful for any help ! 10Q