Noise often has a distinctive spectrum and amplitude. These can be used to characterize the noise in an inversion process. Chapters and show how inversion may be used to separate signal and noise using filters and amplitude characteristics of both the signal and noise. This can be especially useful when the noise is coherent and is predictable from trace to trace. One of the challenging issues is to avoid an overlap in the characterization of the noise and the signal, and if the overlap occurs, to control it.