A new signal decomposition scheme was suggested to analyze the hot-wire signal in the wake of an oscillating airfoil. In this scheme, the instantaneous velocity is decomposed into the time mean quantity, the periodic compoment due to airfoil motion, the large scale component, and the random fluctuating component. In order to decompose the hot-wire signal, the running average technique was first applied to the signal and the disadvantage of the technique was discussed. As an alternative, use of a frequency domain filtering technique was recommended. Detailed procedures for the frequency domain filtering technique were given and the problems in using it were discussed.