A method of computing beamformer coefficients at a device, the method comprising: receiving audio signals at a microphone array of the device; calculating a covariance matrix for the received audio signals; computing beamformer coefficients based on the calculated covariance matrix for the received audio signals, said beamformer coefficients being for application by a beamformer to the received audio signals for generating a beamformer output; the method characterized by comprising: storing in storing means a plurality of theoretical covariance matrices for a respective plurality of theoretical audio signals, each theoretical covariance matrix being determined by calculating the covariance matrix that would be produced if the received audio signal arrived at the microphone array with the particular attributes of the theoretical audio signal, each theoretical audio signal having its own particular attributes, the particular attributes being the angle and distance (θ, d) from which the theoretical audio signal is received at the microphone array and/or the spectral shape of the theoretical audio signal, the theoretical covariance matrices being for use in computing beamformer coefficients for application by a beamformer to audio signals received at 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 audio signals have the particular attributes of the theoretical audio signals; retrieving the plurality of theoretical covariance matrices from the storing means; and the calculating of the covariance matrix being calculated by performing a weighted sum of the retrieved plurality of theoretical covariance matrices using the determined respective plurality of weights. receiving audio signals at a microphone array of the device; calculating a covariance matrix for the received audio signals; computing beamformer coefficients based on the calculated covariance matrix for the received audio signals, said beamformer coefficients being for application by a beamformer to the received audio signals for generating a beamformer output; the method characterized by comprising: storing in storing means a plurality of theoretical covariance matrices for a respective plurality of theoretical audio signals, each theoretical covariance matrix being determined by calculating the covariance matrix that would be produced if the received audio signal arrived at the microphone array with the particular attributes of the theoretical audio signal, each theoretical audio signal having its own particular attributes, the particular attributes being the angle and distance (θ, d) from which the theoretical audio signal is received at the microphone array and/or the spectral shape of the theoretical audio signal, the theoretical covariance matrices being for use in computing beamformer coefficients for application by a beamformer to audio signals received at 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 audio signals have the particular attributes of the theoretical audio signals; retrieving the plurality of theoretical covariance matrices from the storing means; and the calculating of the covariance matrix being calculated by performing a weighted sum of the retrieved plurality of theoretical covariance matrices using the determined respective plurality of weights. storing in storing means a plurality of theoretical covariance matrices for a respective plurality of theoretical audio signals, each theoretical covariance matrix being determined by calculating the covariance matrix that would be produced if the received audio signal arrived at the microphone array with the particular attributes of the theoretical audio signal, each theoretical audio signal having its own particular attributes, the particular attributes being the angle and distance (θ, d) from which the theoretical audio signal is received at the microphone array and/or the spectral shape of the theoretical audio signal, the theoretical covariance matrices being for use in computing beamformer coefficients for application by a beamformer to audio signals received at 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 audio signals have the particular attributes of the theoretical audio signals; retrieving the plurality of theoretical covariance matrices from the storing means; and the calculating of the covariance matrix being calculated by performing a weighted sum of the retrieved plurality of theoretical covariance matrices using the determined respective plurality of weights.