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;