The present invention provides a signal analyser (100) that is operable to receive one or more signals and then to analyse said signals with respect to particular properties before outputting an indication as to the classification of the signal with respect to each property. Typically this indication is in the form of a plurality of belief index ratings, the magnitude of each belief index rating relating to the likelihood of the corresponding classification being accurate. This is achieved by incrementing or decrementing one or more individual belief index values in response to the identification of predetermined signal features by the signal processing means (102). Which belief index values are incremented or decremented and by how much is determined by the particular signal feature detected. Typically, this data is retrieved from a suitable look up table stored in the data storage means (104). The data storage means (104) is also operable to store a copy of the received signals for future reference.