A method of determining at least one property of a sound field from a plurality of measured sound field parameters obtained from an array of sensors, the method comprising: - obtaining, from respective measurements by sensors of an array of sensors, the sensors being positioned at respective measurement positions, a plurality of measured sound field parameters each indicative of a sound field parameter at a measurement position; - providing a model of a sound field, the model comprising a set of elementary waves and having associated with it a set of model parameters, the set of model parameters comprising a set of magnitude parameters each indicative of a magnitude of one of the elementary waves; - computing, from the model, computed values of the sound field parameter at each of the measurement positions and as a function of said model parameters; - determining a set of parameter values of the model parameters so as to reduce an error measure by performing an iterative minimization process including a plurality of iterations, the error measure comprising an error term operable to compare the computed values and the measured sound field parameters; - computing the property of the sound field from the determined set of model parameters; wherein determining comprises, at one or more current iterations of the iterative minimization process: - computing a set of current values of the model parameters from at least a set of previous values of the model parameters, the previous values resulting from a previous iteration of the iterative process; - selecting a subset of elementary waves from said set of elementary waves; - adjusting the computed current values of the model parameters so as to suppress a magnitude of all elementary waves other than the selected subset of elementary waves. - obtaining, from respective measurements by sensors of an array of sensors, the sensors being positioned at respective measurement positions, a plurality of measured sound field parameters each indicative of a sound field parameter at a measurement position; - providing a model of a sound field, the model comprising a set of elementary waves and having associated with it a set of model parameters, the set of model parameters comprising a set of magnitude parameters each indicative of a magnitude of one of the elementary waves; - computing, from the model, computed values of the sound field parameter at each of the measurement positions and as a function of said model parameters; - determining a set of parameter values of the model parameters so as to reduce an error measure by performing an iterative minimization process including a plurality of iterations, the error measure comprising an error term operable to compare the computed values and the measured sound field parameters; - computing the property of the sound field from the determined set of model parameters; - computing a set of current values of the model parameters from at least a set of previous values of the model parameters, the previous values resulting from a previous iteration of the iterative process; - selecting a subset of elementary waves from said set of elementary waves; - adjusting the computed current values of the model parameters so as to suppress a magnitude of all elementary waves other than the selected subset of elementary waves.