Look this place for a fantastic description:
http://en.wikipedia.org/wiki/Spectral_density#Power_spectral_density ..better
http://en.wikipedia.org/wiki/Spectral_density_estimation …how to calculate
Look this place for a fantastic description:
http://en.wikipedia.org/wiki/Spectral_density#Power_spectral_density ..better
http://en.wikipedia.org/wiki/Spectral_density_estimation …how to calculate