  Taking advantage of the smoothness of CMB Cl power spectra, we derive a
simple and model-independent parameterization of their measurement. It allows
to describe completely the spectrum, ie. provide an estimate of the value and
the error for any real l point at the percent level, down to low l multipole.
We provide this parameterization for WMAP first year data and show that the
spectrum is consistent with the smoothness hypothesis. We also show how such a
parameterization allows to retrieve the Cl spectra from the measurement of
Fourier rings on the sky (Gamma(m)) or from the angular correlation function
(c(theta))
