A method of testing a product for the detection of the presence therein of a defect such as a void or an inclusion, comprises cutting the product and examining the resultant noise for the presence therein of an acoustic component representative of the presence of the inclusion. The method is applied to the processing of metal into slabs, bars, rods, wire strip etc., where the ends must be cropped to remove defective material, specifically to the continuous processing of strip metal where metal strips are joined continuously end-to-end, and where the ends of each strip as rolled may include undesired inclusions such as slag. A leading end piece is cropped by a shear, and the cropping of such pieces is continued until the testing method shows that the material at the place of the cut is free of the undesired inclusions.
