Here k and n are the indices. Integer N states the length of the signal while M expresses the wave-let filters. The View the MathML source is the wave-let vector, obtained by the coefficients of the signal which is transformed by the wavelet filter. Where View the MathML source actually is a vector with k (non-zero) elements, Θk is the threshold value which keeps k largest element number in View the MathML source and keeping all elements to null. For the number of coefficients k , the MDL criterion giving the minimum value is considered as the optimum one. The level of decomposition depends on the signal as well as the wave-let used for decomposition. The Shannon entropy criterion is best suited to find the decomposition at optimum level of the speed error-signal for motor drive applications. For the entropy of a signal x(n)=〚{x〛_1, x_2, x_3……. x_N}, length N can be represented as [5]: