How can i determine the dominant frequency of a real sound signal recorded from microphone dirctly to matlab

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TESFAW
TESFAW 2014-8-7
编辑： Walter Roberson 2018-6-23
I want to plot the line spectra of a sound data recorded from microphone in wav format
I am not sure whether this code gives the right value or not
function line_spectra(z,Fs);
clear all
close all
clc
clf
%Initialize variab
[z,Fs] = wavread(normal_1.wav',2^17);Fs=44100Hz,data sample=131072
N=length(z);
b=bin2dec(fliplr(dec2bin(0:N-1)))+1;
%make it bit reversed order
MC=z(b);
alfa=N/2;
beta=1;
%calculate Twiddle factor
for n=1:N/2
W(n)=exp(-1i*2*pi*(n-1)/N);
Wr(n)=cos(2*pi*(n-1)/N);
Wi(n)=-sin(2*pi*(n-1)/N);
end
%calculate FFT using inplace non-recursive FFT,radix-2
for h=1:(log(N)/log(2));
b=2^(h-1);
a=1;
a0=1;
for d=1:alfa
c=1;
for e=1:beta
temp1=W(c)*MC(a+b);
temp2=MC(a);
MC(a)= MC(a)+temp1;
MC(a+b)=temp2-temp1;
a=a+1;
c=c+alfa;
end
a=a0+2^(h);
a0=a;
end
alfa=alfa/2;
beta=beta*2;
end
s=which('Exh_manifold_T3B.wav');%Modifying the figure window
set(gcf,'color',get(0,'DefaultUIcontrolBackgroundColor'),'NumberTitle',...
'off','Name',s,'Resize','on','Menubar','none');
%calculate the frequency
fr = (0:(N/256)-1)*Fs/N;
%plot the figure
p = abs(MC(1:N/256));
[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(fr,pp,'k')
xlabel('Frequency(Hz','Color','k','FontSize',12);
ylabel('Magnitude','color','k','FontSize',12);
title('Line spectrum plot for defective engine sound ','color','k','FontSize',12);
set(text (170,1660,'Background','b','EdgeColor','r'),'color','k','FontSize',12);
QUESTION
  1. fail to determine the fundamental frequency .
  2. How can I filter it
  3. the reading directly from the plot and from the code p = abs(MC(1:N/256));
[Amax,f] = max(p);
fprintf('Max.Magn. of Amp1. is %6.4f db/n and the freq f is %4.2f\n',Amax,f); not the same
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Image Analyst
Image Analyst 2014-8-11
How about you just call fft() and look for the location (frequency) of the maximum value? Looks like you're doing that - was there any problem with it?
  1 个评论
TESFAW
TESFAW 2014-8-11
Yes,Sir!
the reading from the plot and the value displayed into the
command window is not the same.
I do not know why ...
I think the problem is in my code but I do not know which
one is wrong

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