LPC spectra estimate 
LPC spectra estimate 
Feb 6 2009, 03:26
Post
#1


Group: Members Posts: 99 Joined: 2August 07 From: Shanghai,China Member No.: 45817 
LPC spectra should correspond with the envelope of DFT spectra.
I plot LPC spectra with matlab. The LPC spectra keep the same shape with the envelope of DFT spectra. But it is larger with a offset than the DFT envelope. Why? Where it go wrong? Here is the matlab script which illustrate it. N = 2560; [x,fs] = wavread('lpc.wav',N); % any speech signal can be used p=12; a = lpc(x,p); X =fft(x); X = X(1:N/2+1)'; X = 10*log10(abs(X).^2); Z = fft(a,N); Z = 1./Z(1:N/2+1); Z = 10*log10(abs(Z).^2); figure; plot(X'); hold on; plot(Z,'r'); grid; offset = 10; figure; plot(X+offset); hold on; plot(Z,'r'); grid; 


Feb 18 2012, 23:33
Post
#2


Group: Members Posts: 1 Joined: 18February 12 Member No.: 97241 
Hello i have got a question regarding LPC theory:
e=signal_esti  signal and then we find that Signal(Z)=e/H(Z) with H(Z)=(1+ ai(z(i)+....apz(p)) The problem is that we plot the entry signal, and then we compare it to signal_estimated. so when we say: > [a,e] =lpc(x,p); > > X =fft(x); > X =X(1:N/2+1)'; > X = 10*log10(abs(X).^2); > > Z =fft(a,N); > Z1 =1./Z(1:N/2+1); > > Z = Z1.*sqrt(e*N); =A0% to use sqrt(e*N),not sqrt(e),Why? > Z = 10*log10(abs(Z).^2); when we plot Z, we plot the original signal, and not the estimated signal !!!!!!! Please i am stucked here i can't understand it well. i want to plot the estimated signal in function of error, and now from theory we are ploting the original signal. iS THERE SOMETHING WRONG WITH MY COMPREHENSION, THANKS A LOT 


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