1. A method for estimating a model of an echo signal in an echo canceller comprising at least an adaptive main filter for modeling the echo signal and an adaptive shadow filter for modeling the echo signal, wherein the adaptation speed of the shadow filter is faster than the adaptation speed of the adaptive main filter, the method comprising: determining whether the adaptive shadow filter models the echo signal better than the adaptive main filter, and updating a system noise estimate of the adaptive main filter in response to determining that the adaptive shadow filter models the echo signal better than the adaptive main filter.