A method for inspecting objects by means of ultrasound, wherein reference signals are used as references for test signals in order to establish residual signals indicating flaws in the objects, said method comprising: - inspecting a test object at one or more positions, the inspecting of one position comprises: - positioning a measuring device comprising a plurality of transducers in a selected position on the inspected object, so that the ultrasonic transducers are in contact with the inspected object, - performing a number of test signal acquisitions at the selected position, each test signal acquisition comprising: - using one transducer of the plurality transducers as a sending probe to induce an ultrasonic signal into the test object, and using at least one other transducer of the transducers as a receiving probe to receive ultrasonic signals from the test object, so that one test signal is obtained for each combination of sending probe and receiving probe; characterized in that said inspecting of one position further comprises: - extracting a direct signal portion of the test signal, wherein the direct signal portion propagates through a zone located between the sending probe and the receiving probe; - determining (105, 205) the influence of contact surface variations between each test signal and corresponding reference signal, wherein the determining (105, 205) of the contact surface variations is based on the direct signal portion of the test signal and a corresponding direct signal portion of the reference signal, and comprises determining a frequency varying filter equivalent for the contact surface; - compensating (106, 206) the full test signal for the contact surface variations by compensating the full test signal on the basis of the determined filter equivalent; and - determining a residual signal based on the compensated test signal for each combination. - inspecting a test object at one or more positions, the inspecting of one position comprises: - positioning a measuring device comprising a plurality of transducers in a selected position on the inspected object, so that the ultrasonic transducers are in contact with the inspected object, - performing a number of test signal acquisitions at the selected position, each test signal acquisition comprising: - using one transducer of the plurality transducers as a sending probe to induce an ultrasonic signal into the test object, and using at least one other transducer of the transducers as a receiving probe to receive ultrasonic signals from the test object, so that one test signal is obtained for each combination of sending probe and receiving probe; - extracting a direct signal portion of the test signal, wherein the direct signal portion propagates through a zone located between the sending probe and the receiving probe; - determining (105, 205) the influence of contact surface variations between each test signal and corresponding reference signal, wherein the determining (105, 205) of the contact surface variations is based on the direct signal portion of the test signal and a corresponding direct signal portion of the reference signal, and comprises determining a frequency varying filter equivalent for the contact surface; - compensating (106, 206) the full test signal for the contact surface variations by compensating the full test signal on the basis of the determined filter equivalent; and - determining a residual signal based on the compensated test signal for each combination.