1. An adaptive filter comprising: a data processing component; an input for receiving input data and for delivering the input data to the data processing component; and an output for outputting information produced by the data processing component, the information representative of a model of the input data, the data processing component configured to produce a model based on Gaussian mixtures by: (i) receiving an input datum; (ii) based on the input datum, identifying one or more Gaussians in a plurality of Gaussians to be updated; and (iii) for each Gaussian to be updated, adjusting its parameters using a 19 1 t &it; - &it; type -type of learning curve having a learning rate which is initially greater than a learning factor &agr; and which converges to &agr; over time.