1. An apparatus comprising: a prefilter for prefiltering an input sample set during periods of no speech activity and during periods of speech activity and prior to noise estimation of a signal, the prefilter being adapted to discard spectral minima in the sample set that are shorter than a specified duration so as to provide a set of samples prefiltered both during periods of no speech activity and during speech activity for noise estimation, wherein the input sample set includes either samples representing spectral magnitudes of the signal or samples representing short term average magnitude values of the signal.