For quality control the FFT can be used in process improvement, nondestructive testing, and defining texture coarseness. In metals and textiles, the use of light scattering as a practical tool of surface finish measurement has the advantage of being non -contacting, sensitive, area sample and inherently absolute. Another quality control technique is nondestructive testing. A good example of this is the testing for cracks in composite materials. By using FFT, the attenuation in a material may be found.
Attenuation is a measure of the decrease in a propagated signal through a substance.
Such is the case of the Uster yarn tester. This instrument measures the periodic fluctuations in the thickness of strands of yarn. Applying an FFT analysis of the thickness versus distance and finding periodic peaks allows manufacturing faults to be located. A further use of the FFT in industry is performance grading. In the manufacture of carpeting the Fourier power spectrum can be used to grade how well the carpeting wears.