from spectrum import modcovar, marple_data, arma2psd, cshift
from pylab import log10, linspace, axis, plot 

a, p = modcovar(marple_data, 15)
PSD = arma2psd(a)
PSD = cshift(PSD, len(PSD)/2) # switch positive and negative freq
plot(linspace(-0.5, 0.5, 4096), 10*log10(PSD/max(PSD)))
axis([-0.5,0.5,-60,0])