1. Training apparatus for training a signal classification analysis apparatus of the type arranged to detect predetermined components of a signal, characteristic of distortion being present in the signal, and for generating a classification indicative of the severity and/or types of distortion present, the training apparatus comprising: means for providing a training sequence comprising a first signal and a distorted version of the first signal, analysis means for extracting individual segments from the training sequence and generating a distortion perception measure for indicating the extent to which the distortion of each segment would be perceptible to a human observer, and means for applying the distortion perception measures and the associated distorted signal segments to the signal classification analysis apparatus to determine the classifications to be applied to subsequently input signals.