1. A method performed by a processor of calculating a similarity metric between a first feature vector of a first audio and/or video signal and a second feature vector of a second audio and/or video signal, the method comprising acts of: calculating a weighting factor that depends on a variance in mean value of a specific one feature per class of signals divided by a variance in value of a specific one feature for a collection of signals; and calculating a distance between the first feature vector and the second feature vector, both the first feature vector and the second feature vector comprising a feature value of a second dimension, wherein the weighting factor that is selected gives a stronger weight to the first dimension than to the second dimension.