How compute the periodogram spectral estimate by fourier transform of autocorrelation function in matlab

I got the autocorrelation function using the command xcorr and found the fourier transform by fft however, the plot looks strange. I think im making a mistake with the formula. Any input will be appreciated. thanks

[Honglei Chen]

Could you post your code snippet? How are you using xcorr?

Answer 1

[Rapheal]

Hi Honglei Chen

I was able to figure out how to get the xcorr correctly and now i'm trying to compute the variance and mean of averaged periodogram and blackman tukey method. Do you have any idea of how i can compute them in matlab?