1. A method 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 the step of: 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 a weighting factor is used that gives a stronger weight to the first dimension than to the second dimension.