  The emissivity of the accretion flow is a key parameter affecting the shape
of both the energy and variability power spectrum of AGN. We explore the
energy-dependence of the power spectrum for five AGN, across the XMM-Newton
bandpass, and across the 0.01-1 mHz frequency range, finding a ubiquitous
flattening of the power spectrum towards higher energies. We develop a
framework to explore this behaviour and thereby extract the energy dependence
of the emissivity assuming a simple disc-like geometry for the inflow. We find
that the emissivity ranges from R^-2 at energies around the soft excess and
increases to R^-4 or steeper above ~4-6 keV. We describe the changing
emissivity index with a linear function in energy, finding the best-fitting
slopes to vary between AGN. We attempt to correlate the slope of the linear
function against key AGN parameters but, as yet, the sample size is too small
to confirm hints of a correlation with Eddington ratio.
