Other contributions to the noise can be from reflections and refracted waves. Instrumental noise also plays a vital role when the power of the applied ultrasonic wave is increased.The dominant noise can be classified into incoherent and coherent noise. Commonly used signal processing technique of temporal averaging reduces the effect of incoherent noise in the signal. Coherent noise is time invariant unlike incoherent noise
which is time varying. Suppressing coherent noise needs advanced signal processing techniques. Signal processing techniques such as split spectrum processing, correlation technique and other transform based techniques such as Fourier and Wavelet Transform
have been proposed to enhance the detectability of defects.Wavelet filtering has proved to be reliable in enhancing the signal quality due to its high correlation with respect to the diffracted waves in TOFD technique. In the early stages of development of
signal processing, lower order wavelets with less number of filter coefficients were used in de-noising of the ultrasonic signals. In this work, higher order wavelets are used for de-noising the ultrasonic signals from the austenitic stainless steel welds and the results are compared with respect to the lower order wavelets.