  We present a method designed to estimate the noise power spectrum in the time
domain for CMB experiments. The noise power spectrum is extracted from the time
ordered data avoiding the contamination coming from sky signal and accounting
the pixellisation of the signal and the projection of the noise when making
intermediate sky projections. This method is simple to implement and relies on
Monte-Carlo simulations, it runs on a simple desk computer. We also propose a
trick for filtering data before making coadded maps in order to avoid ringing
due to the presence of signal in the timelines. These algorithms were
succesfully tested on Archeops data.
