# Preprocessing signal before LPC

I have a signal that contains the speaking of three vowels. The signal is contaminated with dc offset and an interference at 60 Hz. I want to perform LPC for the synthesis of the spoken vowels. Do I have to remove the dc offset and the interference before performing LPC?

My initial signal looks like this:

There is also another question of mine about LPC here https://stackoverflow.com/questions/28909899/weird-output-of-lpc-algorithm

• DC is more than suppressed. it be gone with most HPFs having a gain of $-\infty$ dB at DC. this is more than just an artefact. turns out that because the autocorrelation $R_x[m]$ is the inverse Fourier transform of the power spectrum $S_x[k]$, which is also the square of the magnitude of the spectrum $|X[k]|^2$, removing DC before the autocorrelation insures that $R_x[m]$ is DC free. that means it must go negative for some values (and we know that $R_x[m]>0$ for some values of $m$ (like $m=0$) and gives you a solid threshold for separating peaks in the autocorrelation. – robert bristow-johnson Aug 1 '16 at 4:57