A method of operating a hearing aid system comprising the steps of: - providing a plurality of input signal sets, each consisting of two input signals, wherein each of the input signals represents the output from a microphone; - transforming the input signals from a time domain representation and into a time-frequency domain representation; - estimating an inter-microphone phase difference between the input signals for each of said plurality of input signal sets using the time-frequency domain representation of the input signals; - determining an unbiased mean phase and a mapped mean resultant length, from each of said estimated inter-microphone phase differences, wherein the mean is taken over time; - estimating a time difference of arrival, for each of said input signal sets, using a plurality of unbiased mean phases weighted by a corresponding plurality of reliability measures, wherein each of the reliability measures is derived at least partly from a mapped mean resultant length and wherein each of said time difference of arrivals is estimated based on unbiased mean phases, reliability measures and mapped mean resultant lengths that are all estimated from the same input signal set as said time difference of arrival; - deriving an estimate of a local direction of arrival and a corresponding local reliability measure for each of the estimated time difference of arrivals, wherein the local reliability measures are at least partly derived from the mapped mean resultant lengths and wherein, for each of said estimated time difference of arrivals, the local reliability measure and the mapped mean resultant length are estimated from the same input signal set; - providing an estimate of a common direction of arrival by combining the estimated local directions of arrival and the corresponding local reliability measures; - using the estimate of the common direction of arrival as input to at least one hearing aid system processing stage; wherein the mapped mean resultant length R̃ ab ( k, l) is determined using an expression from a group of expressions of the form given by: R ̃ ab k l = E f e jθ ab k l p k l wherein indices l and k represent respectively the frame used to transform the input signals into the time-frequency domain and the frequency bin; wherein E is an expectation operator; wherein e jθ ab ( k,l) represents the inter-microphone phase difference between the first and the second microphone; wherein p is a real variable; and wherein f is an arbitrary function. - providing a plurality of input signal sets, each consisting of two input signals, wherein each of the input signals represents the output from a microphone; - transforming the input signals from a time domain representation and into a time-frequency domain representation; - estimating an inter-microphone phase difference between the input signals for each of said plurality of input signal sets using the time-frequency domain representation of the input signals; - determining an unbiased mean phase and a mapped mean resultant length, from each of said estimated inter-microphone phase differences, wherein the mean is taken over time; - estimating a time difference of arrival, for each of said input signal sets, using a plurality of unbiased mean phases weighted by a corresponding plurality of reliability measures, wherein each of the reliability measures is derived at least partly from a mapped mean resultant length and wherein each of said time difference of arrivals is estimated based on unbiased mean phases, reliability measures and mapped mean resultant lengths that are all estimated from the same input signal set as said time difference of arrival; - deriving an estimate of a local direction of arrival and a corresponding local reliability measure for each of the estimated time difference of arrivals, wherein the local reliability measures are at least partly derived from the mapped mean resultant lengths and wherein, for each of said estimated time difference of arrivals, the local reliability measure and the mapped mean resultant length are estimated from the same input signal set; - providing an estimate of a common direction of arrival by combining the estimated local directions of arrival and the corresponding local reliability measures; - using the estimate of the common direction of arrival as input to at least one hearing aid system processing stage; wherein indices l and k represent respectively the frame used to transform the input signals into the time-frequency domain and the frequency bin; wherein E is an expectation operator; wherein e jθ ab ( k,l) represents the inter-microphone phase difference between the first and the second microphone; wherein p is a real variable; and wherein f is an arbitrary function.