The present disclosure relates in a first aspect to a method of determining an objective perceptual quantity of a noisy speech signal using directional sound information. The method comprises steps of applying a noisy speech signal comprising a mixture of target speech and interfering noise to a first hearing instrument with an adjustable microphone arrangement and controlling the adjustable microphone arrangement to produce first and second directivity patterns exhibiting first and second directivity indexes, respectively, wherein said second directivity index is smaller than the first directivity index at one or more reference frequencies. First and second noisy speech segments are recorded from the adjustable microphone arrangement using the first and second directivity patterns, respectively, and at least one value of the objective perceptual quantity of the noisy speech signal is determined by comparing the first noisy speech segment and the second noisy speech segment.
