1. A method of computing beamformer coefficients at a device, the method comprising: storing a plurality of theoretical covariance matrices for a respective plurality of theoretical signals in a store, each theoretical signal having its own particular attributes, the theoretical covariance matrices being for use in computing beamformer coefficients for application by a beamformer to signals received at the device; receiving the signals at an input of the device; determining, for the plurality of theoretical covariance matrices, a respective plurality of weights based on an analysis of the extent to which the received signals have the particular attributes of the theoretical signals; retrieving the plurality of theoretical covariance matrices from the store; calculating a covariance matrix set for the received signals by performing a weighted sum of the retrieved plurality of theoretical covariance matrices using the determined respective plurality of weights; and computing beamformer coefficients based on the calculated covariance matrix for the received signals, said beamformer coefficients being for application by the beamformer to the received signals for generating a beamformer output.