1. A voice activity detection system for discriminating between at least two classes of events, the system comprising: feature vector units for determining at least two different feature vectors for each frame of a set of frames containing an input signal, sets of preclassifiers trained for said at least two classes of events for classifying said at least two different feature vectors, a weighting factor value calculator for determining values for at least one weighting factor based on outputs of said preclassifiers for each of said frames, a combined feature vector calculator for calculating a value for the combined feature vector for each of said frames by applying said at least one weighting factor to said at least two different feature vectors, and a set of classifiers trained for said at least two classes of events for classifying said combined feature vector.